Light guide element and display device

Abstract

The invention provides a light guide element and a display device. The light guide element is configured to guide light from the display element to the pupil, and includes: an incident portion into which the light is to be incident; a separation section configured to separate light in a first direction; and an emission part configured to emit light toward the pupil. The separation section has a plurality of separation surfaces having different spectral reflectance from each other. The plurality of separation faces includes a dielectric film having a plurality of layers.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a light guide element and an (image) display device. BACKGROUND

[0002] Japanese Patent Application Publication No. 2024-37843 discloses an image display device including a light guide plate configured to guide a display image to a pupil of an observer.

[0003] In the image display device disclosed in Japanese Patent Application Publication No. 2024-37843, light utilization efficiency is low due to a large amount of unnecessary light. SUMMARY

[0004] One aspect of the present disclosure provides a light guide element configured to guide light from a display element to a pupil. The light guide element includes an entrance portion into which the light is to be incident, a separation portion configured to separate the light in a first direction, and an exit portion configured to exit the light toward the pupil. The separation portion has a plurality of separation surfaces different from each other in spectral reflectance. The plurality of separation surfaces includes a dielectric film having a plurality of layers. A display device having the above light guide element also constitutes another aspect of the present disclosure.

[0005] Another aspect of the present disclosure provides a light guide element configured to guide light from a display element to a pupil. The light guide element includes an entrance portion into which the light is to be incident, a separation portion configured to separate the light in a first direction, and an exit portion configured to exit the light toward the pupil. The separation portion has a plurality of separation surfaces different from each other in spectral reflectance. The plurality of separation surfaces includes at least one separation surface satisfying the following inequality:

[0006] 0.7 ≤ Re(a, n, P) / Re(a, n, S) ≤ 1.6

[0007] wherein, with respect to an nth separation surface among the plurality of separation surfaces counted from the entrance portion, Re(a, n, S) is a reflectance [%] of S-polarized light among light having a principal wavelength in a case where a is an incident angle [°] of a principal ray, and Re(a, n, P) is a reflectance [%] of P-polarized light among light having a principal wavelength in a case where a is an incident angle [°] of a principal ray. A display device having the above light guide element also constitutes another aspect of the present disclosure.

[0008] Another aspect of the present disclosure provides a display device including a display element; and a light guide element configured to guide light from the display element to a pupil. The light guide element includes an entrance portion into which the light is to be incident, a separation portion configured to separate the light in a first direction, and an exit portion configured to exit the light toward the pupil. The following inequalities are satisfied:

[0009] Ly / Li ≥ 0.40

[0010] where Li is an illuminance [lx] of the light of a principal wavelength incident on the entrance portion, and Ly is an amount of light [lx] exiting to an area of an exit pupil in the first direction.

[0011] Further features of various embodiments of the present disclosure will become apparent from the following description of examples with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a configuration diagram of an image display device according to Example 1.

[0013] Figure 2 is a configuration diagram of a light guide plate according to Example 1.

[0014] Figure 3 is a configuration diagram of a light guide plate according to Example 1.

[0015] Figure 4 is a configuration diagram of a light source unit according to Example 1.

[0016] Figure 5A and Figure 5B is a configuration diagram of a light source unit according to Example 1.

[0017] Figure 6 is a configuration diagram of a light guide plate according to Example 2.

[0018] Figure 7 is a configuration diagram of a light guide plate according to Example 3.

[0019] Figure 8 shows reflectivity of the first to third exit surfaces in Example 1 with respect to S-polarized light. DETAILED DESCRIPTION

[0020] Embodiments according to the present disclosure will now be described in detail with reference to the accompanying drawings. Corresponding elements in the respective drawings will be denoted by the same reference numerals, and repetitive description thereof will be omitted.

[0021] Example 1

[0022] An image display device 10 and a light guide plate (light guide element) 11 according to Example 1 of the present disclosure will now be described with reference to Figures 1 to 3 ,Figure 1 is a configuration diagram of the image display device 10. Figure 2 is a configuration diagram of the light guide plate 11 in an xy cross section. Figure 3 is a configuration diagram of the light guide plate 11 in an xz cross section.

[0023] The image display device 10 includes the light guide plate 11 and the light source unit 12. The light guide plate 11 is made of a transparent material such as glass or plastic, and guides image light of a liquid crystal panel (image display element) 44 from the light source unit 12 to a pupil EP. The light guide plate 11 has a first face 11a and a second face 11b which are parallel to each other. The light guide plate 11 also has an entrance portion 13, a separation portion (separator or splitter) 14 having a plurality of separation faces inclined at a predetermined angle (angle θ) with respect to a y axis in an xy cross section, and an exit portion 15 having a plurality of separation faces (exit faces) inclined at a predetermined angle (angle ) with respect to a z axis in an xz cross section.

[0024] Image light enters the entrance portion 13. The separation portion 14 separates the image light in the pupil EP in a first direction (y (axis) direction). The separation portion 14 has a plurality of separation faces different in spectral reflectance (different from each other). The exit portion 15 exits the image light from the light guide plate 11 toward the pupil EP.

[0025] The light guide plate 11 according to this example is made of a glass material whose refractive index is, for example, 1.518, but is not limited to this implementation. The plurality of separation faces have a property of reflecting light at a predetermined angle (angle α) with a predetermined reflectance, and include a plurality of layers (a plurality of dielectric films, that is, a dielectric film composed of a plurality (two or more) of layers) including a high-refractive-index film and a low-refractive-index film. In general, film materials such as TiO2, Ta2O5, and ZnS are used as the high-refractive-index film, and film materials such as SiO2, MgF2, and Al2O3 are used as the low-refractive-index film. In order to improve the transmittance of the outside world, an anti-reflection film is vapor-deposited on each of the first face 11a and the second face 11b.

[0026] Next, the light source unit 12 will be described with reference to Figure 4 . Figure 4is a configuration diagram of the light source unit 12. The light source unit 12 includes RGB laser light sources 41 (41R, 41G, 41B), a cross dichroic prism 42, an illumination optical system 43, a liquid crystal panel (image display element) 44, and a condenser lens 45. RGB laser light (P-polarized light) emitted from the laser light sources 41 is synthesized by the cross dichroic prism 42 and is emitted to the illumination optical system 43. The laser light incident on the illumination optical system 43 uniformly illuminates the liquid crystal panel 44. Image light (S-polarized light) modulated by the liquid crystal panel 44 is condensed on a predetermined position of the light guide plate 11 via the condenser lens 45. Light (P-polarized light) that is not modulated by the liquid crystal panel 44 is absorbed by a polarizing plate (not shown) or the like.

[0027] The P-polarized light and the S-polarized light correspond to the polarization direction defined by the separation surface (emission surface) of the emission portion 15 in the light guide plate 11. In this example, the laser light source 41B has a wavelength of 450 nm, the laser light source 41G has a wavelength of 520 nm, and the laser light source 41R has a wavelength of 640 nm. The dominant wavelength of the laser light source 41 is 520 nm, which has a high relative visibility. The image display device 10 according to this example is configured to emit light of three colors (RGB), but is not limited to this implementation and can be configured to emit monochromatic light using only the laser light source 41G.

[0028] In this example, instead of the liquid crystal panel 44, a reflective liquid crystal panel (LCOS) or a digital mirror device formed of micro mirrors as pixels can be used as the image display element. The light source unit 12 can be configured using a laser light source and a micro electro mechanical system (MEMS). Alternatively, an organic light emitting diode (OLED) or a MicroLED can be used as the light source unit 12.

[0029] Image light polarized in a predetermined direction (S-polarized) emitted from the light source unit 12 is incident on the incident portion 13 of the light guide plate 11, is deflected in a predetermined direction by the reflecting surface 13a, and is each totally reflected by the first surface 11a and the second surface 11b to propagate through the light guide plate 11. Then, the image light is split into a plurality of light beams in the xy cross section by the separation portion 14 (an eye box (exit pupil) in the y direction of the pupil EP of the observer is enlarged), and is guided to the emission portion 15.

[0030] In this example, it is assumed that the angle of the image light incident on the reflecting surface 13a of the incident portion 13 is ±10° (angle within the glass). In Figure 2 , the light ray L22 represents the chief ray in the xy cross section, the light ray L21 represents a light ray of +10° with respect to the chief ray, the light ray L23 represents a light ray of -10° with respect to the chief ray, and the angle γ of the light ray L22 with respect to the y axis is 40° (γ = 40°). In Figure 3In this example, light ray L32 represents a chief ray in the xz cross section, light ray L31 represents a light ray at +10° with respect to the chief ray, and light ray L33 represents a light ray at -10° with respect to the chief ray. The separating section 14 includes a plurality of (15) separating surfaces inclined at an angle θ. A plurality of dielectric films M1 to M15 are formed on the plurality of separating surfaces, respectively. In this example, θ = 20°. However, in this example, the number of dielectric films (separating surfaces) is not limited to 15, and can be other numbers.

[0031] The image light guided to the emission section 15 is split into a plurality of light beams in the xz cross section (an eye box in the second direction (x (axial) direction) of the pupil EP of the observer is enlarged), and is guided to the pupil EP of the observer. The emission section 15 includes a plurality of (12) separating surfaces (emission surfaces) inclined at a predetermined angle The emission section 15 has a plurality of emission surfaces having different spectral reflectances from each other. A plurality of dielectric films M21 to M32 are formed on the plurality of emission surfaces. In this example, θ = 20°. However, in this example, the number of dielectric films (emission surfaces) is not limited to 12, and can be other numbers. The light rays L31, L32, and L33 reflected by the reflecting surface 13a of the incident section 13 have incident angles of 70°, 60°, and 50°, respectively, with respect to the second surface 11b of the light guide plate 11 in the xz cross section. The incident section 13 can include a diffractive element, a metasurface, or a holographic element, or the like.

[0032] Numerical Example 1 shows the reflectance (%) of S-polarized light and P-polarized light with respect to the film incident angle at wavelengths of 450 nm, 520 nm, and 640 nm for the dielectric films M1 to M15 of the separating section 14. An arbitrary reflectance can be used in the space. In this example, the dielectric films M1 to M15 are designed to have approximately the same reflectance for S-polarized light and P-polarized light. Since the light rays L21 to L23 propagate while being totally reflected, it is important to note that the incident angle (°) in the xy cross section of the dielectric film does not coincide with the film incident angle (°) of the dielectric film. For example, in the case where the light ray L32 (chief ray in the xz cross section) is incident on the xy cross section of the dielectric film at incident angles of 60°, 70°, and 80°, the film incident angles are 64.3°, 72.8°, and 81.4°, respectively.

[0033] ​The reason why the reflectivity of S-polarized light and P-polarized light are equal to each other will now be described. The light beams from the incident portion 13 propagate through the light guide plate 11 while being totally reflected by the first face 11a and the second face 11b. Therefore, the relationship between the P-polarized light and the S-polarized light in the separating portion 14 changes depending on whether the light is incident into the dielectric film from the first face 11a or the second face 11b, and the light incident on the separating face of the emission portion 15 can be S-polarized light. In the case where the reflectivity of P-polarized light is significantly lower than the reflectivity of S-polarized light, the amount of image light emitted from the separating portion 14 decreases. On the other hand, in the case where the reflectivity of P-polarized light is significantly higher than the reflectivity of S-polarized light, the amount of P-polarized light, which is an unnecessary light amount, increases in the image light emitted from the separating portion 14, and unnecessary light such as ghost increases.

[0034] The light ray L21 (film incidence angle is 64.3°) is separated (divided) into a plurality of light rays by the first dielectric film M1 to the fifth dielectric film M5. Similarly, the light ray L22 (film incidence angle is 72.8°) is separated into a plurality of light rays by the sixth dielectric film M6 to the tenth dielectric film M10, and the light ray L23 (film incidence angle is 81.4°) is separated into a plurality of light rays by the eleventh dielectric film M11 to the fifteenth dielectric film M15. The plurality of separated light rays are guided to the emission portion 15, and then guided to the pupil EP. Since the light beams in the y direction of the pupil EP can be converged, high light use efficiency can be achieved. For the film incidence angle of 72.8°, the light intensity distribution in the y direction in the pupil EP can be made uniform by increasing the reflectivity from the sixth dielectric film M6 to the tenth dielectric film M10.

[0035] Figure 5A and Figure 5B A design example of the dielectric film M6 is shown. The dielectric film M6 is an alternating film of a high-refractive-index TiO2 film and a low-refractive-index SiO2 film, which has 34 film layers. The total film thickness of SiO2 is 1250 nm, and the total film thickness of TiO2 is 1190 nm. At the principal wavelength of 520 nm of green (G) light and the principal wavelength of 640 nm of red (R) light, the reflectivity of S-polarized light and the reflectivity of P-polarized light at the film incidence angles of 72.8° to 79.6° are approximately the same, and are inclined at a predetermined reflectivity. Blue (B) light having a principal wavelength of 450 nm also exhibits similar characteristics. The other dielectric films also include an alternating film of a high-refractive-index TiO2 film and a low-refractive-index SiO2 film.

[0036] The image light (S-polarized light) emitted from the separating section 14 is totally reflected and propagates through the light guide plate 11, and then is divided into a plurality of light beams by the emitting section 15, and is guided to the pupil EP of the observer. The emitting section 15 includes the twenty-first dielectric film M21 to the thirty-second dielectric film M32. Like the separating section 14, the dielectric films M21 to M32 include the alternating films of the high refractive index TiO2 and the low refractive index SiO2. Numerical example 2 shows the reflectance (%) of the S-polarized light with respect to the incident angle of the dielectric films M21 to M32 of the separating section 14 at the principal wavelengths of 450 nm, 520 nm, and 640 nm. The space indicates an arbitrary reflectance.

[0037] The first light ray L31 (the incident angle is 70°) is separated into a plurality of light rays by the twenty-second dielectric film M21 to the twenty-sixth dielectric film M26, and is guided to the pupil EP. The second light ray L32 (the incident angle is 60°) passes through the twenty-first dielectric film M21 to the twenty-third dielectric film M23, is separated into a plurality of light rays by the twenty-fourth dielectric film M24 to the thirtieth dielectric film M30, and is guided to the pupil EP. The third light ray L33 (the incident angle is 50°) passes through the twenty-first dielectric film M21 to the twenty-sixth dielectric film M26, is separated into a plurality of light rays by the twenty-seventh dielectric film M27 to the thirty-second dielectric film M32, and is guided to the pupil EP. Thus, the light beams can be converged on the pupil EP, and a high light use efficiency can be achieved.

[0038] Now, let ωV be the field of view angle [°] in the first direction (y direction, vertical direction) at the pupil EP, and let ωH be the field of view angle [°] in the second direction (x direction, horizontal direction). The position of the pupil EP is the position of the eye relief and is usually located at a position 10 mm to 30 mm apart from the emitting section of the light guide plate 11. In this example, the eye relief is 20 mm. In the case where the eye relief value is specified in the specifications, the value in the specifications can be used.

[0039] This example places a mask having an opening of 2 mm x 2 mm at the position of the eye relief (the eye relief is 20 mm in this example), and defines the range in which all the light rays having the field of view angle ωV in the first direction are incident as the eye box size in the first direction. Similarly, the range in which all the light rays having the field of view angle ωH in the second direction are incident is defined as the eye box size in the second direction. In the case where the eye box value is specified in the specifications, the value in the specifications can be used.

[0040] The conditions in this example will now be described.

[0041] The angle θ (absolute value) (°) of the separating section 14 with respect to the y direction can satisfy the following inequality (1):

[0042] 5 ≤ θ ≤ 35 (1)

[0043] In a case where θ becomes lower than the lower limit of the inequality (1), the dielectric film becomes approximately parallel to the y-axis, and it becomes difficult to separate the light. On the other hand, in a case where θ becomes higher than the upper limit of the inequality (1), the angle difference in the yz cross section becomes significantly expressed as a difference in the film incidence angle, and it is difficult to obtain the desired performance.

[0044] The inequality (1) can be replaced by the following inequality (1a):

[0045] 7 ≤ θ ≤ 30 (1a)

[0046] The inequality (1) can be replaced by the following inequality (1b):

[0047] 10 ≤ θ ≤ 25 (1b)

[0048] The following inequality (2) can be satisfied:

[0049] nH ≥ 2.00

[0050] nL ≤ 1.60 (2)

[0051] where nH is the refractive index of the dielectric film having the highest refractive index for light having a principal wavelength, and nL is the refractive index of the dielectric film having the lowest refractive index for light having a principal wavelength. In other words, nH is the maximum value of the refractive index of the plurality of separation surfaces for light having a principal wavelength, and nL is the minimum value of the refractive index of the plurality of separation surfaces for light having a principal wavelength.

[0052] For the desired performance, a refractive index difference between the refractive index of the high refractive index film and the refractive index of the low refractive index film can be provided.

[0053] The inequality (2) can be replaced by the following inequality (2a):

[0054] nH ≥ 2.10

[0055] nL ≤ 1.55 (2a)

[0056] The inequality (2) can be replaced by the following inequality (2b):

[0057] nH ≥ 2.20

[0058] nL ≤ 1.50 (2b)

[0059] The separation portion 14 has the first separation surface (M3), the second separation surface (M8), and the third separation surface (M13) as the plurality of separation surfaces. However, in this example, the first separation surface to the third separation surface are not limited to the dielectric films M3, M8, and M13, and can be any dielectric film in order of proximity to the incidence portion 13.

[0060] Among the plurality of separation surfaces, an nth (n = 1, 2, 3) separation surface is an nth separation surface counted from the incident portion 13.

[0061] The plurality of separation surfaces can include at least one of a separation surface in which the refractive index with respect to light of the main wavelength is greater than or equal to 2.0 and the thickness (Hn) of the dielectric film is greater than or equal to 100 nm, and a separation surface in which the refractive index with respect to light of the main wavelength is less than or equal to 1.6 and the thickness (Ln) of the dielectric film is greater than or equal to 100 nm.

[0062] Hn≥100

[0063] Ln≥100 (3)

[0064] For the desired performance, a high refractive index film and a low refractive index film of a plurality of layers of a predetermined thickness or more can be used. This example can satisfy the following inequality (4):

[0065] H2≥100

[0066] L2≥100 (4)

[0067] The inequality (4) can be replaced by the following inequality (4a):

[0068] H2≥400

[0069] L2≥400 (4a)

[0070] The inequality (4) can be replaced by the following inequality (4b):

[0071] H2≥700

[0072] L2≥700 (4b)

[0073] This example can satisfy the following inequalities (5) and (6):

[0074]

[0075] L3 ≥ 100 (6)

[0076] The inequalities (5) and (6) can be replaced by the following inequalities (5a) and (6a):

[0077] H1≥400

[0078] L1≥400(5a)

[0079] H3≥400

[0080] L3≥400(6a)

[0081] Inequalities (5) and (6) can be replaced by the following inequalities (5b) and (6b):

[0082] H1≥ 700

[0083] L1≥ 700 (5b)

[0084] H3≥ 700

[0085] L3≥ 700 (6b)

[0086] For desired performance, the number of film layers of the second separation surface (M8) can be greater than or equal to 10, greater than or equal to 15, or greater than or equal to 20.

[0087] The plurality of separation surfaces can include at least one separation surface that satisfies the following inequality (7):

[0088] 0.7 ≤ Re(a, n, P) / Re(a, n, S) ≤ 1.6 (7)

[0089] where Re(a, n, S) is the reflectance [%] for S-polarized light in light having a principal wavelength when a is the incident angle [°] of a principal ray, and Re(a, n, P) is the reflectance [%] for P-polarized light in light having a principal wavelength when a is the incident angle [°] of a principal ray, with respect to the n-th separation surface from the entrance portion counted in the plurality of separation surfaces.

[0090] In a case where Re(a, n, P) / Re(a, n, S) becomes lower than the lower limit of inequality (7), the amount of light decreases. On the other hand, in a case where Re(a, n, P) / Re(a, n, S) becomes higher than the upper limit of inequality (7), unwanted light such as ghosting increases.

[0091] This example can satisfy the following inequality (8):

[0092] 0.7 ≤ Re(a, 2, P) / Re(a, 2, S) ≤ 1.6 (8)

[0093] Inequality (8) can be replaced by the following inequality (8a):

[0094] 0.8 ≤ Re(a, 2, P) / Re(a, 2, S) ≤ 1.4 (8a)

[0095] Inequality (8) can be replaced by the following inequality (8b):

[0096] 0.9 ≤ Re(a, 2, P) / Re(a, 2, S) ≤ 1.2 (8b)

[0097] The example can satisfy at least one of the following inequalities (9) and (10):

[0098] 0.7 ≤ Re(a, 1, P) / Re(a, 1, S) ≤ 1.6 (9)

[0099] 0.7 ≤ Re(a, 3, P) / Re(a, 3, S) ≤ 1.6 (10)

[0100] The inequalities (9) and (10) can be replaced by the following inequalities (9a) and (10a):

[0101] 0.8 ≤ Re(a, 1, P) / Re(a, 1, S) ≤ 1.4 (9a)

[0102] 0.8 ≤ Re(a, 3, P) / Re(a, 3, S) ≤ 1.4 (10a)

[0103] The inequalities (9) and (10) can be replaced by the following inequalities (9b) and (10b):

[0104] 0.9 ≤ Re(a, 1, P) / Re(a, 1, S) ≤ 1.2 (9b)

[0105] 0.9 ≤ Re(a, 3, P) / Re(a, 3, S) ≤ 1.2 (10b)

[0106] The emission portion 15 has a first emission surface (M23), a second emission surface (M26), and a third emission surface (M30) as the plurality of emission surfaces. However, in this example, the first to third emission surfaces are not limited to the dielectric films M23, M26, and M30, and can be any dielectric film in order of proximity to the incidence portion 13. It is assumed that, among the plurality of emission surfaces, an m-th (m = 1, 2, 3) emission surface from the incidence portion 13 is an m-th emission surface. The plurality of emission surfaces can include at least one emission surface that satisfies the following inequality (11):

[0107] Ro(P, m, P) / Ro(P, m, S) ≤ 0.3 (11)

[0108] where P is an incident angle [°] of a chief ray on the m-th emission surface, Ro(P, m, S) is a reflectance [%] of S-polarized light of light of a principal wavelength on the m-th emission surface, and Ro(P, m, P) is a reflectance [%] of P-polarized light on the m-th emission surface.

[0109] In a case where the value becomes higher than the upper limit of the inequality (11), the transmittance of the outside decreases, and it becomes difficult to achieve a desired quality.

[0110] The example can satisfy the following inequality (12):

[0111] Ro(β, 2, P) / Ro(β, 2, S) ≤ 0.3 (12)

[0112] Inequality (12) can be replaced by the following inequality (12a):

[0113] Ro(β, 2, P) / Ro(β, 2, S) ≤ 0.2 (12a)

[0114] Inequality (12) can be replaced by the following inequality (12b):

[0115] Ro(β, 2, P) / Ro(β, 2, S) ≤ 0.1 (12b)

[0116] The example can satisfy at least one of the following inequalities (13) and (14):

[0117] Ro(β, 1, P) / Ro(β, 1, S) ≤ 0.3 (13)

[0118] Ro(β, 3, P) / Ro(β, 3, S) ≤ 0.3 (14)

[0119] Inequalities (13) and (14) can be replaced by the following inequalities (13a) and (14a):

[0120] Ro(β, 1, P) / Ro(β, 1, S) ≤ 0.2 (13a)

[0121] Ro(β, 3, P) / Ro(β, 3, S) ≤ 0.2 (14a)

[0122] Inequalities (13) and (14) can be replaced by the following inequalities (13b) and (14b):

[0123] Ro(β, 1, P) / Ro(β, 1, S) ≤ 0.1 (13b)

[0124] Ro(β, 3, P) / Ro(β, 3, S) ≤ 0.1 (14b)

[0125] Assuming nG is the refractive index of the light guide element, and ωV is the field of view angle (°) on the cross section having the first direction. The first separation surface can satisfy the following inequality:

[0126] Re(α+ωV / nG, 1, P) > 1.1×Re(α, 1, P) (15)

[0127] Further, the plurality of separation surfaces can include at least one separation surface satisfying the following inequality:

[0128] Re(a, n, P) > 1.1 x Re(a - ωv / nG, n, P) (16)

[0129] In a case where the inequalities (15) and (16) are not satisfied, it becomes difficult to converge the image light on the desired eyebox or to maintain the light use efficiency.

[0130] The example can satisfy the following inequality (17):

[0131] Re(a + ωv / nG, 1, P) > 1.1 x Re(a, 1, P) (17)

[0132] The inequality (17) can be replaced by the following inequality (17a):

[0133] Re(a + ωv / nG, 1, P) > 1.5 x Re(a, 1, P) (17a)

[0134] The inequality (17) can be replaced by the following inequality (17b):

[0135] Re(a + ωv / nG, 1, P) > 2.0 x Re(a, 1, P) (17b)

[0136] The example can satisfy the following inequality (18):

[0137] Re(a, 2, P) > 1.1 x Re(a - ωv / nG, 2, P) (18)

[0138] The inequality (18) can be replaced by the following inequality (18a):

[0139] Re(a, 2, P) > 1.5 x Re(a - ωv / nG, 2, P) (18a)

[0140] The inequality (18) can be replaced by the following inequality (18b):

[0141] Re(a, 2, P) > 2.0 x Re(a - ωv / nG, 2, P) (18b)

[0142] In the example, the field of view angle of the pupil EP can be greater than or equal to 30°. The light condensing effect in the example is particularly effective in an image display device having a large field of view angle where the light use efficiency is significantly reduced. The field of view angle can be greater than or equal to 35°, or greater than or equal to 40°.

[0143] The following inequality (19) can be satisfied:

[0144] LVH / LVL ≤ 2.5 (19)

[0145] where LVH is a maximum value of average illuminance in a case where a distribution of illuminance [lx] of the eyebox is divided into five equal parts in the y direction, and LVL is a minimum value of the average illuminance.

[0146] In a case where the inequality (19) is not satisfied, the illuminance is significantly uneven, and it becomes difficult to obtain a desired image quality.

[0147] The inequality (19) can be replaced by the following inequality (19a):

[0148] LVH / LVL≤ 2.0 (19a)

[0149] The inequality (19) can be replaced by the following inequality (19b):

[0150] LVH / LVL≤ 1.6 (19b)

[0151] The following inequality (20) can be satisfied:

[0152] Ly / Li≥ 0.40 (20)

[0153] where Li is illuminance [lx] of a main wavelength incident on the incidence part 13, and Ly[lx] is illuminance emitted to a region of the eyebox in the y direction (width in the x direction is not defined).

[0154] In a case where the inequality (20) is not satisfied, it becomes difficult to obtain a desired light use efficiency, and the image display device displays a dark image.

[0155] The inequality (20) can be replaced by the following inequality (20a):

[0156] Ly / Li≥ 0.50 (20a)

[0157] The inequality (20) can be replaced by the following inequality (20b):

[0158] Ly / Li≥ 0.60 (20b)

[0159] The following inequality (21) can be satisfied:

[0160] |Ly1-Ly2| / (Ly1+Ly2)≥ 0.5 (21)

[0161] where Ly1[lx] is illuminance (width in the x direction is not defined) of polarized light in a first direction (P-polarized light) emitted to a region of the eyebox (exit pupil) in the y direction, and Ly2[lx] is illuminance of polarized light in a second direction (S-polarized light).

[0162] In cases where inequality (21) is not satisfied, unwanted light, such as ghosting, increases.

[0163] Inequality (21) can be replaced by the following inequality (21a):

[0164] |Ly1-Ly2| / (Ly1+Ly2)≥0.65 (21a)

[0165] Inequality (21) can be replaced by the following inequality (21b):

[0166] |Ly1-Ly2| / (Ly1+Ly2)≥0.80 (21b)

[0167] The light source unit 12 emits RGB visible light image light. It is assumed that the peak wavelength in the wavelength range of 500nm to 580nm (red band) is the first wavelength, the peak wavelength in the wavelength range of 590nm to 670nm (green band) is the second wavelength, and the peak wavelength in the wavelength range of 430nm to 490nm (blue band) is the third wavelength. Furthermore, it is assumed that Ei1 is the amount of light of the first wavelength incident on the injection section 13 [W / mm²]. 2 Ei2 is the amount of light of the second wavelength incident on the injection section 13, and Ei3 is the amount of light of the third wavelength incident on the injection section 13. Ey1 is the amount of light of the first wavelength emitted into the region of the eyebox (exit pupil) in the y direction, Ey2 is the amount of light of the second wavelength emitted into the region of the eyebox in the y direction, and Ey3 is the amount of light of the third wavelength emitted into the region of the eyebox in the y direction. Then, the following inequalities (22) to (24) can be satisfied:

[0168] Ey1 / Ei1≥0.40 (22)

[0169] Ey2 / Ei2≥0.40 (23)

[0170] Ey3 / Ei3≥0.40 (24)

[0171] Inequalities (22) to (24) can be replaced by the following inequalities (22a) to (24a):

[0172] Ey1 / Ei1≥0.50 (22a)

[0173] Ey2 / Ei2≥0.50 (23a)

[0174] Ey3 / Ei3≥0.50 (24a)

[0175] Inequalities (22) to (24) can be replaced by the following inequalities (22b) to (24b):

[0176] Ey1 / Ei1≥ 0.60 (22b)

[0177] Ey2 / Ei2≥ 0.60 (23b)

[0178] Ey3 / Ei3≥ 0.60 (24b)

[0179] The following inequality (25) can be satisfied:

[0180] Lx / Li ≥ 0.40 (25)

[0181] where Lx is an illuminance [lx] of an area of an eyebox shot in an x direction (a width in a y direction is not defined).

[0182] In a case where the inequality (25) is not satisfied, it becomes difficult to obtain a desired light use efficiency, and an image display device displays a dark image.

[0183] The inequality (25) can be replaced with the following inequality (25a):

[0184] Lx / Li≥ 0.50 (25a)

[0185] The inequality (25) can be replaced with the following inequality (25b):

[0186] Lx / Li≥ 0.60 (25b)

[0187] The following inequalities (26) to (28) can be satisfied:

[0188] Ex1 / Ei1 ≥ 0.40 (26)

[0189] Ex2 / Ei2 ≥ 0.40 (27)

[0190] Ex3 / Ei3 ≥ 0.40 (28)

[0191] where Ex1 is an amount of light [W / mm2] of a first wavelength shot in an x direction to an area of an eyebox, Ex2 is an amount of light [W / mm2] of a second wavelength shot in an x direction to an area of an eyebox, and Ex3 is an amount of light [W / mm2] of a third wavelength shot in an x direction to an area of an eyebox. 2 ] Ex2 is an amount of light [W / mm 2 ] of a second wavelength shot in an x direction to an area of an eyebox, and Ex3 is an amount of light [W / mm 2 ] of a third wavelength shot in an x direction to an area of an eyebox.

[0192] The inequalities (26) to (28) can be replaced with the following inequalities (26a) to (28a):

[0193] Ex1 / Ei1≥ 0.50 (26a)

[0194] Ex2 / Ei2≥ 0.50 (27a)

[0195] Ex3 / Ei3≥ 0.50 (28a)

[0196] Inequalities (26) to (28) can be replaced by the following inequalities (26b) to (28b):

[0197] Ex1 / Ei1≥ 0.60 (26b)

[0198] Ex2 / Ei2≥ 0.60 (27b)

[0199] Ex3 / Ei3≥ 0.60 (28b)

[0200] The following inequality (29) can be satisfied:

[0201] Rmin / Rmax≤ 0.20 (29)

[0202] where Rmax is the maximum reflectance of the average of the reflectance of the separation portion 14 to P-polarized light and the reflectance to S-polarized light in the chief ray of the principal wavelength, and Rmin is the minimum reflectance of the average of the reflectance of the separation portion 14 to P-polarized light and the reflectance to S-polarized light in the chief ray of the principal wavelength.

[0203] Inequality (29) can be replaced by the following inequality (29a):

[0204] Rmin / Rmax≤ 0.15 (29a)

[0205] Inequality (29) can be replaced by the following inequality (29b):

[0206] Rmin / Rmax≤ 0.10 (29b)

[0207] In this example, the plurality of separation surfaces includes at least one separation surface that satisfies the following inequalities (30) and (31):

[0208] Re(a, n, P)≤ 10.0 (30)

[0209] Re(a, n, S)≤ 10.0 (31)

[0210] In the case where inequalities (30) and (31) are not satisfied, the amount of unnecessary light that illuminates the area outside the eyebox increases.

[0211] The first separation surface (M3) can satisfy the following inequalities (32) and (33):

[0212] Re(a, 1, P)≤ 10.0 (32)

[0213] Re(a, 1, S) < 10.0 (33)

[0214] Inequalities (32) and (33) can be replaced by the following inequalities (32a) and (33a):

[0215] Re(a, 1, P) < 7.0 (32a)

[0216] Re(a, 1, S) < 7.0 (33a)

[0217] Inequalities (32) and (33) can be replaced by the following inequalities (32b) and (33b):

[0218] Re(a, 1, P) < 4.0 (32b)

[0219] Re(a, 1, S) < 4.0 (33b)

[0220] In designing the dielectric film, the following inequality (34) can be satisfied:

[0221] 0.00 < W / R < 0.03 (34)

[0222] where R is the center wavelength [nm] of at least one spectrum of the light beam emitted from the light source, and W is the full width at half maximum (FWHM) [nm] of the spectrum.

[0223] In this example, the center wavelength R is 450 nm, 520 nm, or 640 nm, which is the main wavelength of the laser source 41. In the case where the value becomes higher than the upper limit of inequality (34), the film design becomes difficult to achieve a predetermined reflectivity over a wide wavelength range, the light utilization efficiency decreases, and the non-uniformity of brightness increases.

[0224] Inequality (34) can be replaced by the following inequality (34a):

[0225] 0.00 < W / R < 0.02 (34a)

[0226] Inequality (34) can be replaced by the following inequality (34b):

[0227] 0.000 < W / R < 0.015 (34b)

[0228] In this example, the emission portion 15 can be configured as follows.

[0229] For example, in Figure 3 , assume that the light rays having the incident angles θ1, θ2, and θ3 (θ1+5 < θ2 < θ3-5) on the first surface 32a are the first light ray L31, the second light ray L32, and the third light ray L33, respectively. Among them, It is the angle [°] of each separation surface relative to the normal of the first surface 11a (second surface 11b), and the angle of incidence of the q-th ray (q: natural number) from the first surface 11a to the separation surface (emission surface). yes The angle of incidence of the q-th ray from the second surface 11b to the separation surface (emission surface) yes For example, angle The angle is 30°, and the incident angles θ1, θ2, and θ3 are 50°, 60°, and 70° respectively, and the incident angle... and These are 70°, 60°, 50°, 10°, 0°, and -10°, respectively. The second ray L32 is at the center of the beam propagating within the light guide plate 11.

[0230] The first ray L3 is split into multiple rays by dielectric films M21 through M27 and guided to the pupil EP. The second ray L32 passes through dielectric films M21 through M23, is split into multiple rays by dielectric films M24 through M30, and is guided to the pupil EP. The third ray L33 passes through dielectric films M21 through M26, is split into multiple rays by dielectric films M27 through M32, and is guided to the pupil EP. Therefore, the light beam can be focused on the pupil EP, and high light utilization efficiency can be achieved.

[0231] The 24th dielectric film M24 is the first ejection surface, the 27th dielectric film M27 is the second ejection surface, and the 30th dielectric film M30 is the third ejection surface. None of the first, second, and third surfaces are parallel to the first direction. When d (mm) is the size of the eye box, the surface that passes through or is closest to the normal from the center of the eye box is the second ejection surface. The surface that passes through or is closest to the normal at position d / 2 in the negative x-direction from the center of the eye box is the first ejection surface, and the surface that passes through or is closest to the normal at position d / 2 in the positive x-direction from the center of the eye box is the third ejection surface. Figure 8 This shows the reflectivity of S-polarized light at the incident angle for the dominant wavelength at the first to third exit surfaces. Assume p (p: 1, 2, 3) represents the order of the exit surfaces (first, second, and third). θ is the angle [°] of the p-th exiting surface relative to the normal of the first surface. q Rs1 is the angle of incidence [°] of the q-th ray (where q is a natural number) incident on the first surface, and Rs1 pq Is the p-th ejection surface about having The reflectivity (%) of the dominant wavelength light at the incident angle [°]. Then the first to the third exiting surfaces can satisfy the following inequalities (35) to (37):

[0232] Rs1 21 >Rs1 22 >Rs1 23 (35)

[0233] Rs1 31 <Rs1 32 (36)

[0234] Rs1 33 <Rs1 32 (37)

[0235] In a case where the inequality (35) is not satisfied, luminance unevenness significantly occurs, and in a case where the inequalities (36) and (37) are not satisfied, the transmittance of external light increases.

[0236] The inequalities (35) to (37) can be replaced with the following inequalities (35a) to (37a):

[0237] Rs1 21 >1.2×Rs1 22 >1.2×Rs1 23 (35a)

[0238] 1.2×Rs1 31 <Rs1 32 (36a)

[0239] 1.2×Rs1 33 <Rs1 32 (37a)

[0240] The inequalities (35) to (37) can be replaced with the following inequalities (35b) to (37b):

[0241] Rs1 21 >1.4xRs1 22 >1.4×Rs1 23 (35b)

[0242] 1.4×Rs1 31 <Rs1 32 (36b)

[0243] 1.4×Rs1 33 <Rs1 32 (37b)

[0244] Since the twenty-first dielectric film M21 to the thirty-third dielectric film M33 have film properties that combine the properties of a polarization separation film and a half mirror film, the refractive index nG of the substrate can be low in order to perform polarization separation at an incident angle ψ12 of 60°. More specifically, the following inequality (38) can be satisfied:

[0245] nG≤ 1.70 (38)

[0246] In a case where nG becomes higher than the upper limit of the inequality (38), the Brewster condition cannot be satisfied, and the transmittance of the external light will be significantly reduced.

[0247] The inequality (38) can be replaced by the following inequality (38a):

[0248] nG≤ 1.65 (38a)

[0249] The inequality (38) can be replaced by the following inequality (38b):

[0250] nG≤ 1.60 (38b)

[0251] Numerical examples 3 and 4 are variations of the separation portion 14 of the present example. Numerical example 3 is a numerical example in which the number of types of dielectric films is reduced from 15 to 8. Numerical example 4 is a numerical example in which the illuminance distribution is more uniform. Numerical example 3 shows a structure in which the same dielectric film is arranged on every two separation faces, but this is not limited to this implementation, and the same dielectric film can be arranged on every three or every four separation faces.

[0252] This example shows a structure in which a dielectric film is formed on the separation faces between the separation portion 14 and the emission portion 15, but this structure can use a fine structure such as a metasurface or a holographic element.

[0253] Example 2

[0254] A light guide plate 61 according to Example 2 of the present disclosure will now be described with reference to Figure 6 A light guide plate 61 according to Example 2 of the present disclosure will now be described with reference to Figure 6 is a structural diagram of the light guide plate 61 according to this example. The light guide plate 61 includes an entrance portion 63, a separation portion 64 having a plurality of separation faces inclined at a predetermined angle in an xy cross section, and an emission portion 65 having a plurality of separation faces inclined at a predetermined angle in an xz cross section. As in Example 1, the separation portion 64 is vapor-deposited with a first dielectric film M1 to a fifteenth dielectric film M15. The separation portion 64 is configured to reduce unnecessary separation faces that do not contribute to converging image light on an eyebox, and this example can reduce unnecessary light and improve light utilization efficiency.

[0255] Example 3

[0256] A light guide plate 71 according to Example 3 of the present disclosure will now be described with reference to Figure 7 A light guide plate 71 according to Example 3 of the present disclosure will now be described with reference to Figure 7is a structural diagram of a light guide plate 71 according to this example. The light guide plate 71 includes an entrance portion 73, a separation portion 74 having a plurality of separation surfaces inclined at a predetermined angle in an xy cross section, an exit portion 75 having a plurality of separation surfaces inclined at a predetermined angle in an xz cross section, and a reflection surface 76. Similar to Example 1, the separation portion 74 is vapor-deposited with the first dielectric film M1 to the fifteenth dielectric film M15. By reflecting image light from the entrance portion 73 with the reflection surface 76, the light guide plate 71 can have a reduced size.

[0257] Numerical Example 1

[0258]

[0259] Numerical Example 2

[0260]

[0261] Numerical Example 3

[0262]

[0263] Numerical Example 4

[0264]

[0265] Each example can provide a light guide element and an image display device with improved light use efficiency. Furthermore, each example can improve brightness distribution and reduce unevenness in light quantity.

[0266] Other Embodiments

[0267] Embodiments of the present application can also be implemented by a method in which a computer (central processing unit (CPU), micro processing unit (MPU)) of a system or an apparatus reads out and executes software (computer program) stored in storage medium (e.g., computer program product) to function in accordance with the above-described embodiments, by providing the software to the system or the apparatus through a network or the like. Furthermore, the software (computer program) can be transmitted from a server computer, etc. to a client computer, etc.

[0268] While the present disclosure has been described with reference to typical embodiments, it is to be understood that the present disclosure is not limited to the typical embodiments. The scope of the claims should be construed to include all such modifications and equivalent structures and functions.

Claims

1. A light guide element configured to guide light from a display element to a pupil, the light guide element comprising: An injection section, wherein the light is to be injected into the injection section; A separation section configured to separate the light in a first direction; as well as An emission section is configured to emit light toward the pupil. The separation section has multiple separation surfaces with different spectral reflectivities, and The plurality of separation surfaces include a dielectric film having multiple layers.

2. The light guide element according to claim 1, wherein, The following inequalities must be satisfied: 5≤θ≤35 Wherein, θ is the angle [°] of the plurality of separation surfaces relative to the first direction.

3. The light guide element according to claim 1, wherein, The following inequalities must be satisfied: nH≥2.00 nL≤1.60 Wherein, nH is the maximum value of the refractive index of the plurality of separating surfaces for the dominant wavelength of light, and nL is the minimum value of the refractive index of the plurality of separating surfaces for the dominant wavelength of light.

4. The light guide element according to claim 1, wherein, The plurality of separation surfaces include at least one of the following: a separation surface with a refractive index greater than or equal to 2.0 for the dominant wavelength and a dielectric film thickness greater than or equal to 100 nm; and a separation surface with a refractive index less than or equal to 1.6 for the dominant wavelength and a dielectric film thickness greater than or equal to 100 nm.

5. The light guide element according to claim 1, wherein, The ejection section has multiple ejection surfaces with different spectral reflectivities.

6. A light guide element configured to guide light from a display element to a pupil, the light guide element comprising: An injection section, wherein the light is to be injected into the injection section; A separation section configured to separate the light in a first direction; as well as An emission section is configured to emit light toward the pupil. The separation section has multiple separation surfaces with different spectral reflectivities, and Wherein, the plurality of separation surfaces includes at least one separation surface that satisfies the following inequality: 0.7≤Re(α,n,P) / Re(α,n,S)≤1.6 Among the plurality of separation surfaces, the nth separation surface counted from the injection point is Re(α,n,S), which is the reflectivity (%) of S-polarized light in light with the main wavelength when α is the incident angle of the main ray (°), and Re(α,n,P), which is the reflectivity (%) of P-polarized light in light with the main wavelength when α is the incident angle of the main ray (°).

7. The light guide element according to claim 6, wherein, The ejection section has multiple ejection surfaces with different spectral reflectivities, and Wherein, the plurality of ejection surfaces includes at least one ejection surface that satisfies the following inequality: Ro(β,m,P) / Ro(β,m,S)≤0.3 Among the plurality of exiting surfaces, the m-th exiting surface counted from the entrance portion, Ro(β,m,S) ​​is the reflectivity (%) of S-polarized light in the main wavelength light when β is the incident angle of the main ray (°), and Ro(β,m,P) is the reflectivity (%) of P-polarized light in the main wavelength light when β is the incident angle of the main ray (°).

8. The light guide element according to claim 6, wherein, When nG is the refractive index of the light guide element and ωV is the field of view (°) on the cross section having the first direction, The first separating surface satisfies the following inequality: Re(α+ωV / nG,1,P)>1.1×Re(α,1,P), and The plurality of separating surfaces includes at least one separating surface that satisfies the following inequality: Re(α,n,P)>1.1×Re(α-ωV / nG,n,P).

9. The light guide element according to claim 6, wherein, The separating surface includes at least one separating surface that satisfies the following inequality: Re(α,n,P)≤10.0 Re(α,n,S)≤10.

0.

10. The light guide element according to claim 1, wherein, The following inequalities must be satisfied: Rmin / Rmax≤0.20 Wherein, Rmax is the maximum average reflectance of the separation section for P-polarized light and S-polarized light in the main ray of the main wavelength, and Rmin is the minimum average reflectance of the separation section for P-polarized light and S-polarized light in the main ray of the main wavelength.

11. The light guide element according to claim 1, further comprising a first surface and a second surface parallel to each other. in, The ejection section has a first ejection surface, a second ejection surface, and a third ejection surface, wherein each of the first ejection surface, the second ejection surface, and the third ejection surface is not parallel to the first surface. Wherein, the first emission surface, the second emission surface, and the third emission surface have different spectral reflectivities than each other, and Among them, the following inequalities are satisfied: θ1+5<θ2<θ3-5 Rs1 21 >Rs1 22 >Rs1 23 Rs1 31 <Rs1 32 Rs1 33 <Rs1 32 Where p represents the order of the ejection surfaces among the first ejection surface, the second ejection surface, and the third ejection surface. θ is the angle [°] of the p-th exiting surface relative to the normal of the first surface. q Rs1 is the angle of incidence [°] of the q-th ray incident on the first surface, where q is a natural number and Rs1 pq Is the p-th ejection surface about having The reflectance (%) of the dominant wavelength of light at the incident angle [°].

12. A display device comprising: The light guide element according to any one of claims 1 to 11; as well as The display element.

13. A display device comprising: Display elements; as well as A light guide element, configured to direct light from the display element to the pupil. The light guide element includes: An injection section, wherein the light is to be injected into the injection section; A separation section, configured to separate the light in a first direction; and An emission section is configured to emit light toward the pupil. Among them, the following inequalities are satisfied: Ly / Li ≥ 0.40 Wherein, Li is the illuminance [lx] of the dominant wavelength light incident on the injection portion, and Ly is the amount of light [lx] emitted into the region of the exit pupil in the first direction.

14. The display device according to claim 13, wherein, The separation section has multiple separation surfaces with different spectral reflectivities.

15. The display device according to claim 14, wherein, The following inequalities must be satisfied: 5≤θ≤35 Wherein, θ is the angle [°] of the plurality of separation surfaces relative to the first direction.

16. The display device according to claim 15, wherein, The following inequalities must be satisfied: |Ly1-Ly2| / (Ly1+Ly2)≥0.5 Wherein, Ly1 is the illuminance [lx] of the polarized light emitted in the first direction toward the region of the exit pupil in the first direction, and Ly2 is the illuminance [lx] of the polarized light in the second direction.

17. The display device according to claim 13, wherein, The following inequalities must be satisfied: Ey1 / Ei1≥0.40 Ey2 / Ei2≥0.40 Wherein, Ei1 is the amount of light incident on the injection portion as the first wavelength, which is the peak wavelength in the red band [W / mm]. 2 Ei2 is the amount of light incident on the injection point at the second wavelength, which is the peak wavelength in the green band [W / mm]. 2 Ey1 is the amount of light of the first wavelength emitted into the region of the exit pupil in the first direction [W / mm]. 2 ], and Ey2 is the amount of light of the second wavelength emitted toward the region of the exit pupil in the first direction.

18. The display device according to claim 13, wherein, The following inequalities must be satisfied: Lx / Li≥0.40 Wherein, Lx is the illuminance [lx] emitted into the region of the exit pupil in the second direction perpendicular to the first direction.

19. The display device according to claim 17, wherein, The following inequalities must be satisfied: Ex1 / Ei1≥0.40 Ex2 / Ei2≥0.40 Wherein, Ex1 is the amount of light of the first wavelength emitted into the region of the exit pupil in the second direction perpendicular to the first direction [W / mm]. 2 ], and Ex2 is the light intensity of the second wavelength [W / mm 2 ].

20. The display device according to any one of claims 13 to 19, wherein, The following inequalities must be satisfied: 0.00 <W / R<0.03 Where R is the center wavelength [nm] of at least one spectrum of the light beam emitted from the light source, and W is the full width at half maximum (FWHM) of the spectrum [nm].

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