Optical system and head-up display device

Abstract

To provide an optical system and a head-up display device which can suppress heat generation of a picture display element.SOLUTION: The optical system sequentially includes: a light source; a polarizer; a picture display element; an analyzer for an optical path OP1 for light source light emitted from the light source. The picture display element sequentially includes a color filter, a reflective polarizer RP1, and a liquid crystal layer LC1 for the optical path OP1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical system and a head-up display device. [Background technology]

[0002] In recent years, the use of head-up display devices as vehicle image display devices has been expanding. Head-up display devices are installed on the dashboard of a vehicle and can display driving information as a virtual image by projecting image light onto the windshield as a projection plate.

[0003] Various configurations of head-up display devices have been considered. For example, Patent Document 1 proposes that an image display device having a specific configuration be used as a head-up display device. This image display device has an image display device, which has a liquid crystal display panel and a light source, and the liquid crystal display panel has a liquid crystal cell and polarizing plates (polarizer and analyzer) attached to both sides of the liquid crystal cell. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 082920 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the image display device described in Patent Document 1, the direction of the polarization reflection axis of the reflective polarizer used as a reflector can be easily adjusted, which is advantageous in that it is possible to improve the uniformity of the brightness of the image projected on the projection plate. On the other hand, in the liquid crystal display panel of the image display device in such an image display device, when external light (typically sunlight) is incident on the polarizer from the opposite direction to the light that displays the image, the polarizer tends to absorb the light and generate heat. From the viewpoint of suppressing such heat generation and further improving the quality of the image display device, there is still room for improvement in the technology described in Patent Document 1.

[0006] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide an optical system and a head-up display device capable of suppressing heat generation from an image display element. [Means for solving the problem]

[0007] As a result of extensive research, the inventors discovered that the above problems could be solved by devising an appropriate arrangement of the components in an optical system, and thus completed the present invention.

[0008] That is, the present invention includes the following aspects. [1] A light source; A polarizer; An image display element; An analyzer, are provided in this order for an optical path OP1 of the light source light emitted from the light source, The optical system, wherein the image display element includes a color filter, a reflective polarizer RP1, and a liquid crystal layer LC1, in this order, along the optical path OP1. [2] the analyzer includes an absorptive polarizing plate AP1 having an incident surface for external light, The optical system according to [1], wherein the image display element and the analyzer are inclined with respect to the optical path OP1 and / or the optical path OP2 of the external light. [3] the image display element further includes a liquid crystal layer LC2 disposed on the polarizer side of the liquid crystal layer LC1, the liquid crystal layer LC2, the color filter, the reflective polarizer RP1, and the liquid crystal layer LC1 are arranged in this order with respect to the optical path OP1, The optical system according to [1] or [1], wherein the pixel size of the liquid crystal layer LC2 is larger than the pixel size of the liquid crystal layer LC1. [4] The optical system according to [3], wherein the image display element further comprises a reflective polarizer RP2 between the liquid crystal layer LC2 and the color filter. [5] The optical system according to any one of [1] to [3], wherein the polarizer is spaced apart from the image display element and is inclined with respect to the optical path OP1. [6] The optical system described in any of [1] to [5], wherein the polarizer comprises a reflective polarizing plate RP3, a reflective polarizing plate RP4, and an absorptive polarizing plate AP2 arranged between the reflective polarizing plate RP3 and the reflective polarizing plate RP4. [7] The absorptive polarizing plate AP2 has a substrate S1, The optical system according to [6], wherein a thickness retardation value a of the base material S1 in the absorptive polarizing plate AP2 is 40 nm or less. [8] The optical system according to [6] or [7], wherein the reflective polarizer RP3 and the reflective polarizer RP4 are wire grid polarizers having a wire grid structure on their surfaces. [9] The optical system according to any one of [6] to [8], wherein the sum of a thickness retardation value b1 of a substrate of the reflective polarizing plate RP3 and a thickness retardation value b2 of a substrate of the reflective polarizing plate RP4 is 40 nm or less.

[10] The optical system further includes an inner wall having an irradiation surface for light of the light source reflected by the polarizer, The optical system according to any one of [1] to [9], wherein at least a portion of the irradiation surface includes a light-reflecting material.

[11] The optical system according to any one of [1] to

[10] , wherein the image light emitted through the analyzer includes vehicle driving information.

[12] A head-up display device comprising the optical system according to any one of [1] to

[11] . Effect of the Invention

[0009] According to the present invention, it is possible to provide an optical system and a head-up display device capable of suppressing heat generation from an image display element. [Brief description of the drawings]

[0010] [Figure 1] 1 is an explanatory diagram showing an application example of a head-up display device. [Diagram 2] FIG. 1 is a schematic diagram illustrating a first embodiment of an optical system. [Diagram 3] FIG. 2 is a schematic diagram illustrating a second embodiment of the optical system. [Figure 4] FIG. 2 is a schematic diagram illustrating a third embodiment of an optical system. [Diagram 5] FIG. 11 is a schematic diagram illustrating a fourth embodiment of an optical system. [Figure 6] FIG. 13 is a schematic diagram illustrating a fifth embodiment of an optical system. [Figure 7] FIG. 13 is a schematic diagram of an example of further details of a fifth embodiment of the optical system; [Figure 8] FIG. 2 is a schematic diagram illustrating a polarizer having an absorptive polarizing plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a mode for carrying out the present invention (hereinafter also referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the present embodiment, and can be carried out in various modified forms within the scope of the gist of the present invention. Note that the same elements are given the same reference numerals, and duplicated explanations may be omitted. Furthermore, in the drawings, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings, unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to the ratios shown in the drawings.

[0012] The optical system of this embodiment includes a light source, a polarizer, an image display element, and an analyzer, in this order, along an optical path OP1 of light source light emitted from the light source, and the image display element includes a color filter, a reflective polarizer RP1, and a liquid crystal layer LC1, in this order, along the optical path OP1. Since the optical system of this embodiment is configured in this way, it is possible to suppress heat generation from the image display element. The optical system of this embodiment can be preferably applied as a head-up display device. Hereinafter, each component of the optical system of this embodiment will be described in detail based on an example in which the optical system of this embodiment is applied as a head-up display device.

[0013] Fig. 1 is an explanatory diagram illustrating a head-up display device including the optical system of this embodiment. As illustrated in Fig. 1, a head-up display device 1 including an optical system 10 is provided, for example, on a dashboard 2 of a vehicle. The head-up display device 1 projects image light (display light) 3 onto a windshield 4 serving as a projection board, and can display driving information as a virtual image 5. A driver 6 can view the virtual image 5 by superimposing it on the scenery seen through the windshield 4. Examples of the projection board include the windshield of an automobile and a semi-transparent plate called a combiner.

[0014] FIG. 2 shows an example of the first embodiment of the optical system. 2, the optical system 10 includes a light source 20, a polarizer 21, an image display element 22, and an analyzer 23, in this order, on an optical path OP1 of the source light L1 emitted from the light source 20 (i.e., along the optical path OP1 of the source light L1). As illustrated in FIG 2, the image display element 22 includes a color filter CF, a reflective polarizing plate RP1, and a liquid crystal layer LC1, in this order, on the optical path OP1. As illustrated in FIG. 2, the analyzer 23 has an incident surface 23a for the external light L2. In this embodiment, the reflective polarizing plate transmits one polarized light among the incident visible light and reflects the other polarized light. The reflective polarizing plate in this embodiment preferably has a unique polarization axis that does not change the polarization direction of the polarized light that is transmitted and reflected depending on the direction and angle of the incident visible light. In addition, in this embodiment, it is preferable to use a polarizing plate having a unique polarization axis as the analyzer, and in particular, an absorptive polarizing plate that absorbs the other polarized light can be preferably adopted. When such an absorptive polarizing plate is provided, unnecessary light as image light among the polarized light transmitted through the polarizer 21 can be absorbed and cut, and as a result, the generation of stray light tends to be prevented. In this embodiment, for example, the polarization axis directions of the polarizer and the analyzer are arranged orthogonally to each other, so that the light source light modulated by the image display element can be polarized and separated to generate an image. As illustrated in FIG. 2, the analyzer 23 may have a flat plate shape and be bonded to the surface (outside) of the image display element 22 opposite to the light source 20. In addition, the polarization axis means the polarization transmission axis and the polarization reflection axis in a reflective polarizing plate, and the polarization transmission axis and the polarization absorption axis in an absorptive polarizing plate. In addition, when two polarizing plates are superimposed in the direction in which light enters and transmits, and are arranged so that the directions of the polarization transmission axes are perpendicular to each other, the polarization axis directions are said to be perpendicular. As illustrated in FIG. 2, the external light L2 enters the analyzer 23 from the incident surface 23a, passes through the analyzer 23, and then reaches the image display element 22. In the image display element 22, the color filter CF and the reflective polarizer RP1 are arranged in this order with respect to the optical path OP1 (the reflective polarizer RP1 is arranged closer to the external light side than the color filter CF), so that at least a part of the external light L2 is reflected as a polarized component by the reflective polarizer RP1 before reaching the color filter CF. The reflected external light L2' passes through the liquid crystal layer LC1 and the analyzer 23 in the opposite direction to the external light L2 and is guided out of the optical system 10. When the external light L2 reaches the color filter CF, the color filter CF tends to absorb the light, that is, convert light energy into thermal energy, causing the color filter CF to generate heat. In the optical system of this embodiment, each component is arranged as described above, so that external light L2 can be reflected by the reflective polarizing plate RP1 before it reaches the color filter CF, thereby suppressing heat generation in the image display element (heat generation in the color filter CF).

[0015] In the example of FIG. 2, the light source light L1 emitted from the light source 20 enters the polarizer 21, and at least a part of the light source light L1 passes through the polarizer 21 and enters the image display element 22. Next, the light source light L1 is modulated by the image display element 22, and is polarized and separated by the analyzer 23 to become image light. In the example of FIG. 1, this image light is projected onto the windshield 4 as a projection board, and driving information is displayed as a virtual image 5. The driver 6 can view the virtual image 5 by superimposing it on the scenery through the windshield 4. That is, in this embodiment, the image light emitted through the analyzer can include vehicle driving information.

[0016] As described above, the first aspect has been described using the example shown in FIG. 2, but the details of the light source 20, the polarizer 21, the image display element 22 (color filter CF, reflective polarizer RP1, and liquid crystal layer LC1), and the analyzer 23 are not limited to those shown in FIG. 2, and the optical system of this embodiment includes a light source, a polarizer, an image display element, and an analyzer in this order relative to the optical path OP1, and as long as the image display element includes a color filter, a reflective polarizer RP1, and a liquid crystal layer LC1 in this order relative to the optical path OP1, the heat generation of the image display element (heat generation in the color filter CF) can be suppressed. The second to fifth aspects of the optical system described below also include the same configuration as the first aspect, and therefore, like the first aspect of the optical system described above, the heat generation of the image display element (heat generation in the color filter CF) can be suppressed.

[0017] FIG. 3 shows an example of the second embodiment of the optical system. As illustrated in FIG. 3, the optical system 10 may include a light source 20, a polarizer 21, an image display element 22, and an absorptive polarizing plate AP1 as an analyzer, in this order along an optical path OP1. As illustrated in FIG. 3, the image display element 22 may include a color filter CF, a reflective polarizer RP1, and a liquid crystal layer LC1 in this order with respect to the optical path OP1. In the example of FIG. 3, the absorptive polarizer AP1 has an incident surface AP1a of the external light L2, and the external light L2 is incident on the absorptive polarizer AP1 from the incident surface AP1a, passes through the absorptive polarizer AP1, and then reaches the image display element 22. Here, as illustrated in FIG. 3, in the optical system 10, the image display element 22 and the absorptive polarizer AP1 may be inclined with respect to the optical path OP1 of the light source light L1 and / or the optical path OP2 of the external light L2, and it is preferable that the image display element 22 and the absorptive polarizer AP1 are inclined with respect to the optical path OP2 of the external light L2. Here, "inclined" with respect to the optical path OP1 means that at least a part of the light source light L1 that reaches the image display element 22 via the polarizer 21 is polarized and reflected in a direction away from the optical path OP1. In addition, "inclined" with respect to the optical path OP2 means that at least a part of the external light L2 that reaches the image display element 22 via the absorptive polarizer AP1 is arranged to be polarized and reflected in a direction away from the optical path OP2. That is, when the image display element 22 and the absorptive polarizer AP1 are inclined, the external light L2' reflected as a polarized component by the reflective polarizer RP1 tends to be guided out of the optical path of the image light, and as a result, the influence of the external light L2' on the image quality tends to be reduced. The inclination angle of the image display element 22 and the absorptive polarizer AP1 is not particularly limited, but may be inclined so that the angle between the optical path OP2 of the external light L2 and the incident surface AP1a is 1 to 45 degrees. In this embodiment, from the viewpoint of making it easier to guide the reflected external light L2' out of the optical path of the image light, it is preferable that the angle between the optical path OP2 of the external light L2 and the incident surface AP1a is inclined so that the angle is 3 to 35 degrees. As described above, when the image display element 22 and the absorptive polarizer AP1 are inclined, it is preferable to design the optical system 10 in consideration of the influence on the optical characteristics caused by the viewing angle dependency inherent to the image display element 22. As an example, in this embodiment, the optical system 10 may further include an optical compensation plate CP. The optical compensation plate CP has a function of suppressing the deterioration of the optical characteristics, and various known ones can be adopted. More specifically, as the optical compensation plate CP, for example, a stretched product of anisotropic resin such as cycloolefin polymer (COP) or polycarbonate (PC) or a laminate of cholesteric liquid crystals can be adopted. In this embodiment, the optical compensation plate CP can be disposed at any position on the optical path OP1, but in terms of design, it is preferable to dispose it on the polarizer 21 side of the image display element 22, as exemplified in FIG. 3. In addition, when the optical compensation plate CP is disposed on the polarizer 21 side of the image display element 22, an absorptive polarizer AP' may be disposed between the optical compensation plate CP and the polarizer 21. 2, in this embodiment, the image display element 22 and the absorptive polarizer AP1 do not have to be inclined with respect to the optical path OP2 of the external light L2. In this case, fluctuations in the optical characteristics caused by the viewing angle dependency inherent to the image display element 22 are less likely to occur.

[0018] FIG. 4 shows an example of the optical system according to the third embodiment. As illustrated in FIG. 4, the optical system 10 includes a light source 20, a polarizer 21, an image display element 22, and an analyzer 23 in this order with respect to an optical path OP1. As illustrated in FIG. 4, the image display element 22 includes a color filter CF, a reflective polarizer RP1, and a liquid crystal layer LC1 in this order with respect to the optical path OP1, and may further include a liquid crystal layer LC2 arranged on the polarizer 21 side of the liquid crystal layer LC1. That is, the liquid crystal layer LC2, the color filter CF, the reflective polarizer RP1, and the liquid crystal layer LC1 may be arranged in this order with respect to the optical path OP1. In the example of FIG. 4, the analyzer 23 has an incident surface 23a for the external light L2, and the external light L2 is incident on the analyzer 23 from the incident surface 23a, passes through the analyzer 23, and then reaches the image display element 22. Here, it is preferable that the pixel size of the liquid crystal layer LC2 is larger than the pixel size of the liquid crystal layer LC1. In this case, the liquid crystal layer LC2 is responsible for switching between the image display area and the image non-display area, and the liquid crystal layer LC1 is responsible for creating the image, so that each can function as such, which improves the image quality (contrast ratio), and as a result, the image display element 22 tends to be able to create higher quality images.

[0019] FIG. 5 shows an example of the optical system according to the fourth embodiment. 5, the optical system 10 includes a light source 20, a polarizer 21, an image display element 22, and an analyzer 23, in this order, with respect to an optical path OP1. As illustrated in FIG 5, the image display element 22 includes a color filter CF, a reflective polarizer RP1, and a liquid crystal layer LC1, in this order, with respect to the optical path OP1, and may further include a liquid crystal layer LC2 arranged on the polarizer 21 side of the liquid crystal layer LC1, and may further include a reflective polarizer RP2 between the liquid crystal layer LC2 and the color filter CF. That is, the liquid crystal layer LC2, the reflective polarizer RP2, the color filter CF, the reflective polarizer RP1, and the liquid crystal layer LC1 may be arranged in this order with respect to the optical path OP1. In the example of FIG. 5, the analyzer 23 has an incident surface 23a for the external light L2, and the external light L2 enters the analyzer 23 from the incident surface 23a, passes through the analyzer 23, and then reaches the image display element 22. Here, it is preferable that the pixel size of the liquid crystal layer LC2 is larger than the pixel size of the liquid crystal layer LC1. In this case, the liquid crystal layer LC2 plays a role in switching between the image display area and the image non-display area, and the liquid crystal layer LC1 plays a role in creating an image, so that the image quality (contrast ratio) is improved, and the image display element 22 tends to be able to create a higher quality image. In addition, when a reflective polarizing plate RP2 is disposed between the liquid crystal layer LC2 and the color filter CF, unnecessary light source light L1 in the image non-display area that has passed through the liquid crystal layer LC2 can be reflected by the reflective polarizing plate RP2 and further reflected by the polarizer 21 to be guided out of the system. The light reflected by the reflective polarizing plate RP2 tends to be suppressed from becoming stray light by at least one of leading out of the system and absorbing by the polarizer (absorption polarizer), and the deterioration of image quality tends to be further suppressed. In addition, the light source light L1 is less likely to reach the image non-display area of ​​the liquid crystal layer LC1, which tends to further suppress unnecessary heat generation. In the example of FIG. 5, the polarization axis direction of the reflective polarizing plate RP2 is preferably parallel to the polarization axis direction of the polarizer . In addition, an absorptive polarizer (not shown in the example of Figure 5) can be provided on the liquid crystal layer LC1 side of the reflective polarizer RP2, and such an absorptive polarizer can have a relatively low polarization separation property that is sufficient to prevent stray light.

[0020] FIG. 6 shows an example of an optical system according to the fifth embodiment. As illustrated in FIG. 6, the optical system 10 includes a light source 20, a polarizer 21, an image display element 22, and an analyzer 23 in this order relative to an optical path OP1, and the image display element 22 includes a color filter CF, a reflective polarizer RP1, and a liquid crystal layer LC1 in this order relative to the optical path OP1. As illustrated in FIG. 6, the polarizer 21 may be separated from the image display element 22 and inclined relative to the optical path OP1. The term "inclined" here means that the polarizer 21 is disposed so that at least a part of the light source light L1 is polarized and reflected in a direction away from the optical path OP1. In other words, when the polarizer 21 is inclined, the light source light L1' reflected by the polarizer 21 as a polarized component tends to be guided out of the optical path of the image light, and as a result, the influence of the external light L1' on the image quality tends to be reduced. The inclination angle of the polarizer 21 is not particularly limited, but may be inclined so that the angle between the optical path OP1 of the source light L1 and the incident surface of the polarizer 21 of the source light L1 is 45 degrees.

[0021] FIG. 7 shows an example of further details of the fifth embodiment of the optical system. As illustrated in Fig. 7, the optical system 10 includes a light source 20, a polarizer 21, an image display element 22, and an analyzer 23, in this order, along an optical path OP1. That is, in the example of Fig. 7, the light source 20, the polarizer 21, the image display element 22, and the analyzer 23 are arranged on a straight line in one direction (the vertical direction Y in Fig. 7). Although not illustrated in the example of Fig. 7, the image display element 22 includes a color filter CF, a reflective polarizing plate RP1, and a liquid crystal layer LC1, in this order, along the optical path OP1. As illustrated in FIG. 7, the optical system 10 may optionally include a first wall 24, a second wall 25, and a third wall . As illustrated in FIG. 7, the polarizer 21 may have a plate shape as a whole. As illustrated in FIG. 7, the polarizer 21 may be disposed so as to be spaced apart from the image display element 22, inclined with respect to the light source light L1 incident from the light source 20, and to reflect at least a part of the external light L2 incident through the image display element 22 via the analyzer 23. In the example of FIG. 7, the polarizer 21 is inclined so that one end 21a (first direction X1 of the horizontal direction X in FIG. 7) approaches the image display element 22 and the other end 21b (second direction X2 of the horizontal direction X in FIG. 7) approaches the light source 20. In the example of FIG. 7, the inclination angle of the polarizer 21 is not particularly limited, but may be inclined at 45 degrees with respect to the horizontal direction X in FIG. 7. It is preferable to adjust the direction of the polarization transmission axis so as to transmit the P wave among the polarized light, but it can be appropriately determined in consideration of the polarization state of the image to be displayed, and is not limited thereto.

[0022] As illustrated in Fig. 7, the polarizer 21 may be formed by stacking two reflective polarizing plates. The polarizer 21 in the example of Fig. 7 includes a reflective polarizing plate RP3 arranged on the image display element 22 side and a reflective polarizing plate RP4 arranged on the light source 20 side. A part of the light source light L1 reflected by the reflective polarizing plate RP4 in the polarizer 21 is incident on and reflected by the second wall surface 25, is reflected again by the reflective polarizing plate RP4, and is reflected by the first wall surface 24. This part of the light source light L1 passes through the polarizer 21, and then passes through the image display element 22 and the analyzer 23 to become image light. On the other hand, at least a part of the external light L2 may pass through the analyzer 23 and the image display element 22 and enter the polarizer 21. The reflective polarizing plate RP3 can polarize and reflect at least a part of such external light L2. The optical system 10 can be configured so that the external light L2 reflected in this way enters the third wall surface 26 and is absorbed or diffused.

[0023] The first wall surface 24, the second wall surface 25, and the third wall surface 26 in the example of Fig. 7 are arranged in a U-shape around the polarizer 21 on the paper surface of the figure. Although not shown in the example of Fig. 7, light-shielding walls can be appropriately provided in front of or behind the paper surface of the figure, thereby preventing stray light, but these are all optional design matters.

[0024] 7, the first wall surface 24 can be disposed around the light source 20 at a position on the light source 20 side of the polarizer 21 (below the polarizer 21 in FIG. 7). The first wall surface 24 may be, for example, parallel to the image display element 22 and directed upward. 7, the second wall surface 25 can be disposed on the end 21a side of the polarizer 21 (first direction X1 of the horizontal direction X of the polarizer 21 in FIG. 7). The second wall surface 25 may be oriented toward the polarizer 21 side (second direction X2).

[0025] As illustrated in FIG. 7, the first wall surface 24 and the second wall surface 25 can be walls on which the light source light L1 reflected by the polarizer 21 is incident. The first wall surface 24 and the second wall surface 25 may be formed in part or in whole from a light-reflective material. The first wall surface 24 and the second wall surface 25 may be, for example, a mirror surface. In this embodiment, the mirror surface means a surface that can reflect light without changing the polarization state. In the case of such a configuration, for example, the light source light L1 reflected by the second wall surface 25 can be returned to the polarizer 21 or the image display element 22 for reuse, which tends to improve the light utilization efficiency.

[0026] As illustrated in FIG. 7, the third wall surface 26 can be disposed on the end 21b side of the polarizer 21 (the second direction X2 of the horizontal direction X of the polarizer 21 in FIG. 7). The third wall surface 26 may be directed toward the polarizer 21 side (the first direction X1). The third wall surface 26 is a wall surface onto which the external light L2 reflected by the polarizer 21 is incident, and a part or the whole of the third wall surface 26 may be formed of a light absorbing material or a member having a structure capable of diffusive reflection. The light absorbing material is, for example, a black material. The member having a structure capable of diffusive reflection is, for example, a wall having a rough surface. In the case of such a configuration, for example, it tends to be possible to prevent the external light L2 reflected by the third wall surface 26 from being re-reflected and becoming stray light.

[0027] As illustrated in FIG. 7, the light source 20 may be arranged so that most of the light source light L1 emitted from the light source 20 is directly incident on the polarizer 21, or the light source 20 may be arranged so that the light source light L1 irradiated on the first wall surface 24 and reflected therefrom is incident on the polarizer 21. The light source in this embodiment is not particularly limited, and for example, a light emitting diode (LED) that emits white light may be used. One type of light source may be used alone, or two or more types may be used in combination. In addition, a plurality of blue, green, and red light emitting diodes may be arranged to combine the light source light L1, or a plurality of white light emitting diodes may be arranged to control the brightness of each area.

[0028] The reflective polarizing plate in this embodiment can be a wire grid polarizing plate (a reflective polarizing plate having a wire grid structure) that has an inherent polarization (reflection) axis and is capable of polarizing and separating light having wavelengths from visible light to infrared light. In this embodiment, the wire grid structure means a structure in which thin metal wires extending in a predetermined direction are aligned. By setting the period of the thin metal wires to about 1 / 3 or 1 / 4 or less of the wavelength of the light to be polarized and separated, it is possible to perform polarization separation such as reflecting polarized light parallel to the thin metal wires and transmitting polarized light perpendicular to the direction. In order to polarize and separate visible light of 400 nm to 700 nm, it is preferable to set the period (pitch) of the thin metal wires of the wire grid structure to 100 nm to 140 nm. This allows appropriate polarization separation of a wide band of external light including infrared light. In addition, by using aluminum as the metal forming the thin wires, it is possible to have polarized reflectivity in a wide band, and it is possible to increase the reflection of external light and light from the light source in the polarizer and reduce absorption, and as a result, it is possible to further suppress the generation of heat in the optical system. It is possible to form a wire grid structure by providing a nano-sized uneven structure extending in a desired direction on the surface of the substrate and depositing a metal film on one side of the convex parts of the periodic uneven structure. In this case, the cross section in the direction in which the concave-convex structure extends is asymmetric because the metal (thin metal wires) are formed on one side of the convex parts on the surface of the substrate. When light is incident on the polarizer at an angle and the P wave is polarized and transmitted, it is preferable to arrange the polarizer so that the light enters the other side where the metal (thin metal wires) of the convex parts is not formed, or the transmitted polarized light exits from that side.

[0029] As illustrated in FIG. 7, the reflective polarizer RP3 may have a base material 40a and a wire grid structure 41a formed on the surface of the base material 40a. As illustrated in FIG. 7, the reflective polarizer RP4 may have a base material 40b and a wire grid structure 41b formed on the surface of the base material 40b. As illustrated in FIG. 7, the reflective polarizer RP3 and the reflective polarizer RP4 are overlapped and bonded to each other such that the wire grid structure 41a and the wire grid structure 41b are located on the outside and the base material 40a and the base material 40b are located on the inside. The reflective polarizer RP3 and the reflective polarizer RP4 can be bonded to each other, for example, by an adhesive or the like. Thus, in this embodiment, it is preferable that the reflective polarizer RP3 and the reflective polarizer RP4 are wire grid polarizers having a wire grid structure on the surface.

[0030] In the example of FIG. 7, the sum of the thickness retardation value b1 of the base material 40a of the reflective polarizer RP3 and the thickness retardation value b2 of the base material 40b of the reflective polarizer RP4 can be set to, for example, 40 nm or less. Here, the thickness retardation value Rth can be measured using a retardation value measuring device (KOBRA-WR, an ellipsometer manufactured by Oji Scientific Instruments Co., Ltd.). In addition, information on the refractive index of the substrate for measuring the thickness retardation value Rth can be obtained by using a refractive index measuring device (Laser Refractive Index Measurement Model 2010, manufactured by Metricon Co., Ltd.) to obtain a wavelength dispersion diagram of the refractive index using Cauchy's dispersion formula from the measurement results of the refractive index at wavelengths of 532 nm, 633 nm, and 824 nm, and then obtaining the refractive index at a wavelength of 550 nm from the wavelength dispersion diagram.

[0031] As illustrated in FIG. 7, when the polarizer 21 includes two wire grid polarizers (reflective polarizer RP3 and reflective polarizer RP4) and is inclined with respect to the light source light L1 incident from the light source 20, the polarizer 21 is influenced by the thickness direction retardation value Rth of the substrate 40, and the transmitted light (amount) tends to be non-uniform in the plane. This is because the polarizer 21 has a wire grid structure serving as a polarization separation layer on both surfaces thereof, and the polarization state of the light transmitted through the substrate changes. Here, when the sum of the thickness direction retardation value b1 of the substrate 40a and the thickness direction retardation value b2 of the substrate 40b of the reflective polarizer RP4 is set to 40 nm or less, the influence of the thickness direction retardation value Rth is suppressed, the polarization state transmitted through the polarizer 21 can be appropriately maintained, and the uniformity of the transmitted light (amount) tends to be ensured. The reflective polarizer RP3 and the reflective polarizer RP4 may be a laminate film or the like in which birefringent films having mutually different birefringences are laminated.

[0032] In the examples of FIGS. 2 to 7, the optical path OP1 of the light source light L1 is parallel to the optical path OP2 of the external light L2, but this embodiment is not limited to the aspect in which the optical path OP1 is parallel to the optical path OP2.

[0033] FIG. 8 illustrates one embodiment of a polarizer in an optical system. 8, the polarizer 21 may include a reflective polarizer RP3, a reflective polarizer RP4, and an absorptive polarizer AP2 disposed between the reflective polarizer RP3 and the reflective polarizer RP4. In this manner, when the absorptive polarizer AP2 is disposed between the reflective polarizer RP3 and the reflective polarizer RP4 in the polarizer 21, there is a tendency that stray light reflected between the reflective polarizer RP3 and the reflective polarizer RP4 can be suppressed when the light source light L1 passes through the polarizer 21. 8, a glass substrate 60 may be provided as a core material between the reflective polarizing plate RP3 and the reflective polarizing plate RP4. When the glass substrate 60 is provided, heat dissipation by thermal conduction becomes possible, and deformation of the polarizer 21 due to heat or impact tends to be prevented. In the example of FIG. 8, the reflective polarizing plate 30, the glass substrate 60, the base material 81, the absorptive polarizing layer 80, the base material 82, and the reflective polarizing plate 30 are arranged in this order from the light source 20 toward the image display element 22. Here, the glass substrate 60 and the absorptive polarizing plate AP2 can be bonded with an adhesive. Similarly, the absorptive polarizing plate AP2 and the reflective polarizing plate 30 can also be bonded with an adhesive. Note that the adhesive is preferably a material with a glass transition point of 0 degrees or less, which is soft and does not orient at room temperature, and for example, an acrylic adhesive, a silicone adhesive, or the like can be appropriately used.

[0034] 8, the absorptive polarizing plate AP2 may have an absorptive polarizing layer 80 and two substrates (substrate 81 and substrate 82) provided on both sides of the absorptive polarizing layer 80. The absorptive polarizing layer 80 is not particularly limited, but may be, for example, a layer obtained by impregnating a dichroic dye or iodine in polyvinyl alcohol and stretching it. The substrates 81 and 82 protect both sides of the absorptive polarizing layer 80, and may be, for example, a film made of triacetyl cellulose, but are not particularly limited. The thickness retardation value Rth of the substrate of the absorptive polarizer AP2 can be 40 nm or less. In this case, there is a tendency that the decrease (unevenness) in the transmittance of the polarizer 21 can be suppressed. Note that, as illustrated in FIG. 8, when the absorptive polarizer AP2 has two substrates (substrate 81 and substrate 82), the sum of the thickness retardation values ​​Rth of the substrate 81 and substrate 82 is preferably 40 nm or less. Note that, when the absorptive polarizer 70 has one substrate (referred to as "substrate S1"), the thickness retardation value a of the substrate S1 itself is preferably 40 nm or less.

[0035] 7 and 8 show examples of the reflective polarizer RP3 and the reflective polarizer RP4 having a wire grid structure on the surface, but in this embodiment, a reflective polarizer without a wire grid structure can also be used. Also, in Fig. 7 and Fig. 8, each of the examples shows an embodiment in which the polarizer 21 has two reflective polarizers (reflective polarizer RP3 and reflective polarizer RP4), but in this embodiment, the polarizer may have one reflective polarizer.

[0036] Further optional configurations of the optical system of this embodiment will be described below.

[0037] In the examples of Figures 2 to 6, the specific configuration of the polarizer 21 is omitted, but the polarizer 21 in these examples may have the configuration illustrated in Figure 8, or may not have the configuration illustrated in Figure 8.

[0038] In particular, in the examples of FIGS. 2 to 6, when the polarizer 21 does not have the configuration illustrated in FIG. 8, the optical system 10 may further include a reflective polarizer RP' not illustrated in FIGS. 2 to 6. In this case, the arrangement of the reflective polarizer RP' is not particularly limited as long as the optical system 10 functions, but for example, the reflective polarizer RP' may be disposed between the light source 20 and the polarizer 21. The reflective polarizer RP' may or may not be in contact with adjacent components. Specific examples of the arrangement of the reflective polarizer RP' include, but are not limited to, the optical system 10 including the light source 20, the reflective polarizer RP', the polarizer 21, the optical compensation plate CP, the color filter CF, the reflective polarizer RP1, the liquid crystal layer LC1, and the absorptive polarizer AP1 in this order with respect to the optical path OP1.

[0039] In the examples of Figs. 2 to 8 (regardless of whether the polarizer 21 has the configuration illustrated in Fig. 8 for the examples of Figs. 2 to 6), the optical system 10 may further include a reflective polarizer RP'' that is a reflective polarizer not shown in each figure and is separate from the reflective polarizer RP'. In this case, the arrangement of the reflective polarizer RP'' is not particularly limited as long as the optical system 10 functions, but can be determined, for example, in relation to a member that divides the inside and outside of the optical system 10 (for example, a dust cover that can be arranged on the external light side on the optical path OP1). For example, the reflective polarizer RP'' may be arranged between the dust cover and the absorptive polarizer AP1 (analyzer 23). The reflective polarizer RP'' may or may not be in contact with the adjacent components. Specific examples of the arrangement of the reflective polarizer RP" include, but are not limited to, an optical system 10 including a light source 20, a polarizer 21, an optical compensation plate CP, a color filter CF, a reflective polarizer RP1, a liquid crystal layer LC1, an absorptive polarizer AP1, and a reflective polarizer RP", in this order along the optical path OP1. In such an example arrangement, the polarization transmission axis of the reflective polarizer RP" can be made the same as the polarization transmission axis of the adjacent absorptive polarizer AP1.

[0040] In this embodiment, the optical system 10 may include both of the above-mentioned reflective polarizer RP' and reflective polarizer RP'', or may include only one of them, as long as it functions as an optical system.

[0041] The optical system of the present embodiment can be preferably applied as a head-up display device. That is, the head-up display device of the present embodiment can include the optical system of the present embodiment. However, the optical system and the head-up display device of the present embodiment can also be applied to things other than vehicles.

[0042] Although the present embodiment has been described above with reference to the accompanying drawings, the present invention is not limited to the present embodiment. Various modifications of the present invention are possible without departing from the spirit of the present invention. For example, some components in one embodiment can be added to other embodiments within the scope of ordinary creativity of a person skilled in the art. Also, some components in one embodiment can be replaced with corresponding components in other embodiments. [Industrial Applicability]

[0043] The present invention is useful in providing an optical system capable of preventing an image display element from becoming too hot. [Explanation of symbols]

[0044] 1 Head-up display device 10 Optical System 20 light source 21 Polarizer 22 Image display element 23 Analyzer CF Color Filter L1 light source light L2 External light LC1 liquid crystal layer LC2 liquid crystal layer RP1 reflective polarizer RP2 reflective polarizer RP3 reflective polarizer RP4 Reflective Polarizer

Claims

1. A light source; A polarizer; An image display element; An analyzer, are provided in this order for an optical path OP1 of the light source light emitted from the light source, The optical system, wherein the image display element includes a color filter, a reflective polarizer RP1, and a liquid crystal layer LC1, in this order, along the optical path OP1.

2. the analyzer includes an absorptive polarizing plate AP1 having an incident surface for external light, The optical system according to claim 1 , wherein the image display element and the analyzer are inclined with respect to the optical path OP1 and / or the optical path OP2 of the external light.

3. the image display element further includes a liquid crystal layer LC2 disposed on the polarizer side of the liquid crystal layer LC1, the liquid crystal layer LC2, the color filter, the reflective polarizer RP1, and the liquid crystal layer LC1 are arranged in this order with respect to the optical path OP1, The optical system of claim 1 , wherein a pixel size of the liquid crystal layer LC2 is larger than a pixel size of the liquid crystal layer LC1 .

4. The optical system according to claim 3 , wherein the image display element further comprises a reflective polarizer RP2 between the liquid crystal layer LC2 and the color filter.

5. The optical system of claim 1 , wherein the polarizer is spaced from the image display element and is tilted with respect to the optical path OP1.

6. The optical system of claim 1 , wherein the polarizer comprises a reflective polarizer RP3, a reflective polarizer RP4, and an absorptive polarizer AP2 disposed between the reflective polarizer RP3 and the reflective polarizer RP4.

7. The absorptive polarizing plate AP2 has a substrate S1, The optical system according to claim 6 , wherein a thickness retardation value a of the base material S1 in the absorptive polarizing plate AP2 is 40 nm or less.

8. The optical system according to claim 6 , wherein the reflective polarizer RP3 and the reflective polarizer RP4 are wire grid polarizers having a wire grid structure on a surface thereof.

9. 9. The optical system according to claim 8, wherein a sum of a thickness retardation value b1 of a substrate of the reflective polarizer RP3 and a thickness retardation value b2 of a substrate of the reflective polarizer RP4 is 40 nm or less.

10. The optical system further includes an inner wall having an irradiation surface for light of the light source reflected by the polarizer, The optical system of claim 1 , wherein at least a portion of the illumination surface comprises a light reflective material.

11. The optical system of claim 1 , wherein the image light emitted through the analyzer includes vehicle driving information.

12. A head-up display device comprising the optical system according to any one of claims 1 to 11.

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