JP2024089261A - Optical Components - Google Patents

Abstract

An optical member that is thinned while ensuring the area of a display viewing zone and visibility of an outside scene.
[Solution] A light guide 2 is provided with an incident surface 2a on which external scene light is incident, an exit surface 2b which reflects the incident light from the incident surface 2a and emits it to the outside, and a reflecting surface 2c which is disposed opposite the exit surface 2b and reflects the reflected light from the exit surface 2b towards the exit surface 2b. The exit surface 2b has a plurality of prism portions 3 which are constituted by a plurality of inclined surfaces 31-33 with different inclinations. The reflecting surface 2c has a reflecting portion 41 which is inclined in the same manner as one of the plurality of inclined surfaces 31-33.
[Selected figure] Figure 2

Description

The present invention relates to an optical element that reflects a portion of light incident on an incident surface internally and emits the incident light and its reflected light to the outside from a surface different from the incident surface.

Conventionally, an example of this type of optical element is that described in Patent Document 1. The optical element described in Patent Document 1 has a light guide having an entrance surface on which external light enters, a first surface to which the external light entering from the entrance surface is initially directed, and a second surface opposite the first surface, and a semi-transparent mirror arranged on the first surface side. In this optical element, a portion of the external light entering from the entrance surface is reflected by the semi-transparent mirror to the second surface, and the remainder is absorbed or transmitted by the semi-transparent mirror, and the second surface reflects the light reflected by the semi-transparent mirror to the second surface side. In addition, this optical element has a prism sheet having multiple prisms arranged on the first surface, and the light transmitted through the semi-transparent mirror is emitted to the outside via the multiple prisms.

Patent No. 6372305

In recent years, there has been a demand for this type of optical element to be thin while ensuring a wide display area (hereinafter referred to as the "display viewing area") on the side of the exit surface where the multiple prisms are arranged, which allows the user to view the scene behind the optical element. The distance between the first and second surfaces of the optical element that are arranged in parallel, i.e., the thickness, is determined by the angle of incidence of the outside light with respect to the first and second surfaces, the width of the display viewing area, and the number of round trips. In order to reduce the thickness of the optical element while ensuring a wide display viewing area, it is necessary to increase the number of times that the incident outside light makes a round trip between the first and second surfaces (hereinafter referred to as the "number of round trips").

However, increasing the number of round trips increases the number of boundaries between adjacent outside scene lights incident on the first surface, i.e., the number of boundaries between adjacent outside scene lights that have made different round trips, which can impair the continuity of the outside scene in the display viewing zone. Furthermore, when the first surface of the optical member is made of a semi-transparent mirror, the luminance of the guided outside scene light that makes more round trips decreases, resulting in a large change in luminance in the display viewing zone. In this way, simply thinning the optical member and increasing the number of round trips of the incident outside scene light makes it difficult to ensure visibility in the display viewing zone.

In view of the above, the present invention aims to provide an optical element that is thin and widens the display viewing zone while ensuring visibility of the outside scene in the display viewing zone.

In order to achieve the above object, the optical element described in claim 1 is an optical element that internally reflects and guides external light, and includes a light guide (2) having an entrance surface (2a) on which the external light is incident, an exit surface (2b) where the incident light from the entrance surface first arrives and reflects the incident light and emits it to the outside, and a reflection surface (2c) that is disposed opposite the exit surface and reflects the reflected light of the incident light reflected at the exit surface toward the exit surface, the exit surface having a plurality of prism portions (3) composed of a plurality of inclined surfaces (31, 32, 33) with different inclinations, and the reflection surface having an identical inclined surface (41) that is a surface with the same inclination as one of the plurality of inclined surfaces.

This optical member includes a light guide having an entrance surface, an exit surface, and a reflecting surface, and includes a plurality of prism portions, the exit surface of which is composed of a plurality of inclined surfaces. The reflecting surface has an identical inclined surface that is inclined to one of the inclined surfaces of the prism portion. According to this, the angle of the light that is reflected by the exit surface and directed toward the reflecting surface after entering the inside of the light guide from the entrance surface becomes larger than the angle of the light directed toward the exit surface inside the light guide. As a result, even if the distance between the reflecting surface and the exit surface, i.e., the thickness, is reduced, the width of one round trip of the incident light between the reflecting surface and the exit surface becomes large, and a wide display viewing area can be secured. In addition, since the width of one round trip of the incident light between the reflecting surface and the exit surface is secured to be greater than a predetermined value, even if the thickness is reduced, it is not necessary to excessively increase the number of round trips inside the light guide. Therefore, this optical member is thinned, and while the display viewing area is widened, the visibility of the outside scene in the display viewing area can be secured.

The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below.

FIG. 2 is a cross-sectional view showing the optical member according to the first embodiment. 3A to 3C are explanatory diagrams illustrating light guide in the optical member according to the first embodiment. FIG. 2 is an enlarged cross-sectional view showing region III in FIG. 1 . 5A to 5C are schematic diagrams showing the relationship between the inclination angle of each inclined surface constituting a prism portion on the exit surface and light guiding. 10A and 10B are diagrams illustrating the inclination angle of the rear surface and the resulting suppression of gaps in light guide. 5A and 5B are schematic diagrams illustrating an optical member and a light guide according to a comparative example. FIG. 6 is a cross-sectional view showing an optical member according to a second embodiment. 13A to 13C are schematic diagrams showing prism portions and widths of first to third regions of an exit surface in a second embodiment. 13A to 13C are explanatory diagrams of light guide in an optical member according to a second embodiment. FIG. 11 is a cross-sectional view showing a first modified example of the optical member of the second embodiment. FIG. 13 is a cross-sectional view showing a second modified example of the optical member of the second embodiment. 12 is an explanatory diagram of light guide in the optical member of FIG. 11 . FIG. 10 is an explanatory diagram of gaps in light rays caused by a reflecting surface having a prism portion; FIG. FIG. 13 is a cross-sectional view showing a third modified example of the optical member of the second embodiment. FIG. 15 is an enlarged cross-sectional view showing region XV in FIG. 14 . FIG. 16 corresponds to FIG. 15 and is an enlarged cross-sectional view showing a cavity layer forming step. FIG. 16 is an enlarged cross-sectional view corresponding to FIG. 15, showing a modified example having a reflective layer instead of a cavity layer. FIG. 11 is a cross-sectional view showing an optical member according to another embodiment.

The following describes embodiments of the present invention with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals.

First Embodiment
The optical member 1 of the first embodiment will be described with reference to the drawings. The optical member 1 of the present embodiment can be used as a blind spot assistance device that is attached to a member or obstacle that blocks the user's view and creates a blind spot, and allows the user to view the scene in the blind spot. For example, in the case of an in-vehicle application, the optical member 1 is attached to a pillar of the vehicle on which it is mounted, and guides external light from the blind spot area caused by the pillar to the user's side, allowing the user to view the scene in the blind spot area.

In FIG. 4, the light entering the optical element 1 and the light exiting the optical element 1 are hatched to make it easier to understand the light guided within the optical element 1.

As shown in FIG. 1, the optical member 1 includes a light guide 2 made of a light-transmitting material. The light guide 2 includes an entrance surface 2a that allows external light to enter the inside, an exit surface 2b adjacent to the entrance surface 2a, a reflecting surface 2c arranged opposite the exit surface 2b, a terminal surface 2d that connects the exit surface 2b and the reflecting surface 2c, and a back surface 2e that connects the entrance surface 2a and the reflecting surface 2c. The optical member 1 allows external light to enter the inside of the light guide 2 from the entrance surface 2a, and while a portion of the incident light is repeatedly reflected between the exit surface 2b and the reflecting surface 2c, the optical member 1 allows the user on the exit surface 2b side to visually recognize the scene in the blind spot area.

Hereinafter, for convenience of explanation, as shown in FIG. 2, the light incident on the light guide 2 from the outside is referred to as "external light L ₁ ", and the light of the external light L ₁ that enters the inside of the light guide 2 from the incident surface 2a is referred to as "incident light". The light of the incident light that directly enters the exit surface 2b from the incident surface 2a is referred to as "first incident light L ₂₁ ", and the reflected light of the incident light that is reflected by a part of the exit surface 2b and heads toward the reflecting surface 2c is referred to as "second incident light L ₂₂ ". In addition, the light of the second incident light L ₂₂ that is reflected by the reflecting surface 2c and heads toward the exit surface 2b is referred to as "third incident light L ₂₃ ". In addition, the light that is emitted to the outside from a part of the exit surface 2b is referred to as "emitted light L ₃ ", and the light that passes through the terminal surface 2d to the outside is referred to as "afterglow L ₄ ".

The light guide 2 is made of a resin material such as polyethylene terephthalate, polycarbonate, polyethylene, acrylic, or a light-transmitting material such as glass. The light guide 2 is designed so that the incident light is totally reflected by the first inclined surface 31 and the reflecting surface 2c of the exit surface 2b, as described later, and guided inside, as shown in FIG. 2. The details will be described later. The light guide 2 is configured so that the maximum thickness Td of the part of the entrance surface 2a is larger than the thickness Ts of the part where the exit surface 2b and the reflecting surface 2c face each other. In other words, the direction in which the incident light travels while being reflected by the exit surface 2b and the reflecting surface 2c is defined as the "light guide direction D1", and the light guide 2 is configured so that the thickness of the part where the exit surface 2b and the reflecting surface 2c face each other in the light guide direction D1 is thinner than the other parts. The light guide direction D1 can also be said to be the direction from the end of the exit surface 2b on the entrance surface 2a side to the end of the end surface 2d side of the exit surface 2b. The maximum thickness Td can also be considered as the height of the incident surface.

The incident surface 2a is a surface that allows the external light _L1 to enter the inside of the light guide body 2. The direction connecting the exit surface 2b and the reflecting surface 2c is defined as the "thickness direction D2", and the incident surface 2a is inclined at an inclination angle ψ (<90°) with respect to the thickness direction D2. The inclination angle ψ of the incident surface 2a is smaller than the light guide angle φ of the first incident light _L21 . The light guide angle φ means the angle between the traveling direction (incident direction) of the first incident light _L21 and the thickness direction D2. If the angle between the traveling direction of the external light _L1 incident on the incident surface 2a and the thickness direction D2 is defined as the "incident angle θ", and ψ<π/2-φ is satisfied according to the refraction condition, the first incident light _L21 is refracted in a direction in which φ is larger than the incident angle θ of the external light _L1 . In other words, when ψ<π/2-φ is satisfied, the first incident light _L21 is guided to a wider range of the exit surface 2b.

As shown in FIG. 3, the exit surface 2b is composed of a plurality of first prism portions 3 each having a first inclined surface 31, a second inclined surface 32, and a third inclined surface 33 with different inclination angles. The exit surface 2b is a prism array in which a plurality of first prism portions 3 are repeatedly arranged along the light guide direction D1. The first prism portion 3 is composed of, for example, a first inclined surface 31, a second inclined surface 32, and a third inclined surface 33 arranged in this order along the light guide direction D1.

The first inclined surface 31 is a surface that reflects the first incident light _L21 and the third incident light _L23 by total reflection, as shown in, for example, FIG. 2 and FIG. 3, and functions as a mirror. The first inclined surface 31 is inclined at an angle α1 with respect to the thickness direction D2, as shown in, for example, FIG. 4. Specifically, the angle α1 of the first inclined surface 31 is larger than the light guide angle φ and less than 90°. The first inclined surface 31 is inclined so that the angle between the traveling direction of the first incident light _L21 and the third incident light _L23 and the normal direction to the first inclined surface 31 is larger than the light guide angle φ. As a result, the first incident light _L21 and the third incident light _L23 are incident on the first inclined surface 31 by satisfying φ<α1, and are reflected by the first inclined surface 31 so that the angle with respect to the thickness direction D2 is ε, which is larger than the light guide angle φ, by satisfying α1<π/2.

In addition, the refractive index of the material constituting the light guide 2 is n, the outside is air (refractive index 1), and the angle between the normal direction to the first inclined surface 31 and the traveling direction of the first incident light _L21 is δ. The light guide 2 is designed to satisfy the following formulas (1) and (2).

sin δ ≧ 1/n (1)
δ=φ+π/2−α1 (2)
This enables the light guide 2 to reflect the first incident light _L21 and the third incident light _L23 by total reflection at the first inclined surface 31 without having a semi-transparent mirror or a mirror made of a material with high reflectivity.

The second inclined surface 32 is a surface adjacent to the first inclined surface 31, and is inclined at an angle β1 different from α1 with respect to the thickness direction D2. The second inclined surface 32 has an inclination angle β1 smaller than the light guide angle φ so that the first incident light _L21 and the third incident light _L23 do not directly enter and cause unintended reflection. As a result, the light of the first incident light _L21 and the third incident light _L23 that does not reach the first inclined surface 31 is incident on the third inclined surface 33 without being blocked by the second inclined surface 32. The second inclined surface 32 may be covered with a light absorbing film (not shown) to suppress the occurrence of ghost images caused by the intrusion of unintended external light.

The third inclined surface 33 is a surface that emits the first incident light _L21 and the third incident light _L23 to the outside as the exit light _L3 , as shown in Fig. 2 or Fig. 4, for example. The third inclined surface 33 is inclined at an angle γ with respect to the thickness direction D2 that is different from α1 and β1, as shown in Fig. 4, for example. It is preferable that the third inclined surface 33 is inclined such that γ is equal to ψ, that is, parallel to the incident surface 2a. This causes the exit light _L3 to be emitted at the same angle as the external scene light _L1 , suppressing the deviation between the scene due to the external scene light _L1 and the scene due to the exit light _L3 , and improving the visibility on the exit surface 2b.

In this embodiment, the reflecting surface 2c has a plurality of second prism portions 4 each consisting of a reflecting portion 41 and an adjacent surface 42 adjacent thereto. The reflecting surface 2c is a prism array in which the plurality of second prism portions 4 are repeatedly arranged along the light guide direction D1.

The reflecting portion 41 is a surface that reflects the second incident light _L22 by total reflection, as shown in FIG. 2, and functions as a mirror. As shown in FIG. 3, the reflecting portion 41 is inclined at an angle α1 with respect to the thickness direction D2, and is the same inclined surface as the first inclined surface 31. That is, the reflecting portion 41 is parallel to the first inclined surface 31. As a result, the incident angle of the second incident light _L22 to the reflecting portion 41 becomes δ, and satisfies the above formula (1). Therefore, the reflecting portion 41 is designed to cause total reflection of the incident light, similar to the first inclined surface 31. The third incident light _L23 reflected by the reflecting portion 41 becomes a light ray with a light guide angle φ, similar to the first incident light _L21 , and heads toward the exit surface 2b.

The adjacent surface 42 is a surface adjacent to the reflecting portion 41, and is inclined with respect to the thickness direction D2 at an angle different from that of the reflecting portion 41. The inclination angle of the adjacent surface 42 with respect to the thickness direction D2 is appropriately adjusted so that, for example, the second incident light _L22 is not directly incident on the adjacent surface 42.

The terminal surface 2d is a surface that connects the emission surface 2b and the reflection surface 2c, and is, for example, an inclined surface inclined at a predetermined angle. A part of the incident light L2 that is repeatedly reflected by the first inclined surface 31 and the reflection portion 41 and does not reach the third inclined surface 33 is emitted to the outside as afterglow _L4 from the terminal surface _2d .

The end face 2d may be subjected to a light-shielding treatment such as disposing a light-absorbing film (not shown). This can suppress the occurrence of ghosts due to leakage of afterglow _L4 . The end face 2d may also be configured to have continuity with the third inclined surface 33 of the end face of the plurality of first prism portions 3 located at the end opposite to the entrance face 2a, that is, may have the same inclination as the third inclined surface 33. In this case, the afterglow _L4 from the end face 2d also becomes the exit light _L3 , and loss of light can be suppressed.

As shown in FIG. 2, the rear surface 2e is an inclined surface that linearly connects the end 2a1 of the incident surface 2a opposite to the exit surface 2b and the end 2c1 of the reflecting surface 2c opposite to the terminal surface 2d. The rear surface 2e is inclined at an angle ξ with respect to the thickness direction D2 that is smaller than the light guide angle φ. As a result, as shown in FIG. 5, a part of the first incident light _L21 passes near the end 2c1, and a part of the second incident light _L22 is incident on the reflecting portion 41 near the end 2c1. In other words, the occurrence of a gap (i.e., a light guide gap) between the first incident light _L21 passing near the end and the third incident light _L23 reflected by the reflecting portion 41 near the end 2c1 is suppressed, thereby improving the visibility of the scene viewed by the user on the exit surface 2b.

The above is the basic configuration of the optical member 1 of this embodiment. With the above-mentioned configuration, the optical member 1 can guide the incident light by total reflection without having a semi-transparent mirror or a mirror made of a material other than the light guide 2. Furthermore, the optical member 1 can ensure a wide display viewing area S on the exit surface 2b while making the thickness Ts of the portion where the exit surface 2b and the reflecting surface 2c face each other thinner than in the past.

The display viewing area S here means the maximum width between the exit lights _L3 at both ends in the light guide direction D1 of the exit surface 2b, as shown in FIG.

Next, the thickness Ts of the optical element 1 will be explained in comparison with the optical element 100 of the comparative example shown in FIG. 6.

The optical member 100 of the comparative example has a light-transmitting light guide 101, similar to the optical member 1, and is configured to guide the outside light _L1 by total reflection without having a semi-transmissive mirror or a mirror made of other materials. The optical member 100 has an incident surface 101a, an exit surface 101b, a reflecting surface 101c, and a terminal surface 101d, and the thickness T of the facing portion of the exit surface 101b between the flat portion 103, which is a light reflecting portion, and the reflecting surface 101c is uniform. In other words, the optical member 100 has a plurality of flat portions 103 and the reflecting surface 101c parallel to each other. The exit surface 101b is formed by repeatedly arranging a prism portion 102 having a surface that emits incident light to the outside, and a flat portion 103 that reflects the incident light by total reflection. The prism portion 102 has an emission portion 102a that emits incident light to the outside, and an adjacent surface 102b that is adjacent to the flat portion 103 on the incident surface 101a side. The optical member 100 is configured such that a first incident light _L21 is reflected by the flat portion 103 at a light guide angle φ to become a second incident light _L22 , and the second incident light _L22 is incident on the reflecting surface 101c at the light guide angle φ and is reflected to the emission surface 101b by total reflection.

In the optical element 100 of the comparative example, the normal direction to the flat portion 103 and the reflecting surface 101c is the thickness direction D2.

Here, in order to ensure a wide display viewing area in the optical element 100, the width in the light guide direction D1 when the incident light makes one round trip between the flat portion 103 and the reflecting surface 101c is defined as the "round trip width W", and it is necessary to ensure that the round trip width W is equal to or greater than a predetermined value. In order to widen the round trip width W, it is necessary to increase the thickness T of the optical element 100. The round trip width W in the optical element 100 is expressed by the following formula (3).

W = 2 × T × tan φ (3)
That is, in order to ensure a predetermined or larger display viewing area, the optical member 100 needs to have the light guide angle φ as large as possible with respect to the incident angle θ, or the thickness T be set to a predetermined or larger value. However, the latter method runs counter to the need for thinning, so the former method is preferable in order to achieve both a sufficient display viewing area and thinning.

Here, the angle between the normal direction to the incident surface 101a and the traveling direction of the external scene light _L1 is α2, the angle between the normal direction and the traveling direction of the first incident light _L21 is β2, and the refractive index of the light guide 101 is _n0 , the light guide angle φ satisfies the following formula (4). In addition, when the inclination angle of the incident surface 101a with respect to the thickness direction D2 is ψ, the following formulas (5) and (6) hold.

sin β2 = sin α2 / n ₀ ... (4)
α2=π/2−θ−ψ (5)
β2=π/2−φ−ψ (6)
According to formulas (4) to (6), in order to make the light guide angle φ as large as possible compared with the incident angle θ, it is necessary to make α2 large. However, when α2 is large, the proportion of the reflected external light _L1 at the incident surface 101a increases, and the proportion of the reflected incident light at the exit portion of the prism portion 102 parallel to the incident surface 101a also increases, which raises concerns about the loss of light rays due to reflection.

For this reason, there is a limit to how thin the thickness T of the optical element 100 can be while still ensuring a specified or greater display viewing area, making it difficult to simultaneously ensure the area of the display viewing area and reduce the thickness.

On the other hand, the reciprocating width W of the optical element 1 is expressed by the following formula (7).

W = Ts × tan ε + Ts × tan φ = Ts (tan ε + tan φ) ... (7)
When the reciprocating width W of the optical element 1 and the comparative optical element 100 are the same, equation (8) holds between the thickness Ts of the optical element 1 and the thickness T of the optical element 100 based on equations (3) and (7).

Ts = 2 × T × tanφ / (tan ε + tan φ) ... (8)
Since the optical member 1 is designed to satisfy φ<ε<π/2, tan ε>tan φ, and tan φ/(tan ε+tan φ) is less than 1/2, i.e., Ts<T. In other words, the optical member 1 has a thinner configuration while ensuring the same display viewing area as the optical member 100. Moreover, unlike the optical member 100, the optical member 1 does not need to increase α2 beyond a predetermined value, and therefore, an effect of suppressing light loss due to reflection at the entrance surface 2a and the third inclined surface 33 can be obtained.

According to this embodiment, the outside scene light _L1 incident on the incident surface 2a at an incident angle θ becomes the first incident light _L21 with a light guide angle φ larger than θ, and the first incident light _L21 becomes the second incident light _L22 with a light guide angle ε larger than φ on the first inclined surface 31 and enters the reflecting portion 41 as the optical member 1. As a result, the optical member 1 can secure the round trip width W required for the incident light to make one round trip between the exit surface 2b and the reflecting surface 2c while reducing the thickness Ts of the portion where the exit surface 2b and the reflecting surface 2c face each other, so that it is possible to secure the display viewing area and to make the optical member 1 thinner. In addition, since the optical member 1 does not have a semi-transparent mirror or a mirror made of a material different from the light guide 2 and guides the incident light by total reflection, the loss of light rays due to light absorption in the light guide 2 is suppressed, and the visibility of the outside scene on the exit surface 2b is improved compared to the conventional art.

Second Embodiment
An optical member 1 according to a second embodiment will be described with reference to the drawings.

The optical member 1 of this embodiment differs from the first embodiment in that the configuration of the exit surface 2b has been changed, as shown in FIG. 7, for example. This difference will be mainly described in this embodiment.

In this embodiment, the exit surface 2b is composed of, for example, a first region 2ba, a second region 2bb, and a third region 2bc from the entrance surface 2a toward the terminal surface 2d. The first region 2ba and the second region 2bb are prism arrays in which a plurality of first prism portions 3 are repeatedly arranged, but the ratio of the width of the first inclined surface 31 to the width from the second inclined surface 32 to the third inclined surface 33 is different. The third region 2bc has the second inclined surface 32 and the third inclined surface 33, and is a prism array in which a plurality of prism portions that do not have the first inclined surface 31 are repeatedly arranged.

For ease of explanation, as shown in FIG. 8, for the first region 2ba and the second region 2bb, the widths of the first inclined surface 31 in the light guide direction D1 are respectively defined as Pa1 and Pa2. Furthermore, for the first region 2ba to the third region 2bc, the widths in the light guide direction D1 from the second inclined surface 32 to the third inclined surface 33 are respectively defined as Pb1, Pb2, and Pb3.

8, the imaginary line connecting both ends of the first prism section 3 and the extension line of the second inclined surface 32 are each shown by a dashed line, and the intersection P between the imaginary line and the extension line is also shown. The imaginary line in FIG. 8 is parallel to the light guide direction D1. The widths Pa1 and Pa2 are the widths from the end of the first inclined surface 31 to the intersection P, and the widths Pb1 and Pb2 are the widths from the intersection P to the end of the third inclined surface 33. In other words, the widths Pa1 and Pa2 are the first widths that contribute to reflection, i.e., the reflection widths. The widths Pb1, Pb2, and Pb3 are the second widths that contribute to emission, i.e., the emission widths. Hereinafter, the ratio of the width (reflection width) of the first inclined surface 31 to the sum of the reflection width and the emission width in the first prism section 3 is referred to as the "reflection width ratio".

The first region 2ba and the second region 2bb are configured such that Pa1/Pb1>Pa2/Pb2 holds. In other words, the first region 2ba is a prism array having a higher ratio of the first inclined surfaces 31 functioning as mirrors than the second region 2bb. That is, the optical member 1 of this embodiment is configured such that the ratio of the first inclined surfaces 31 in the prism array increases in the order of the third region 2bc, the second region 2bb, and the first region 2ba. This makes the amount of light _L3 emitted in each of the regions 2ba to 2bc approximately uniform, and the brightness in the display viewing zone is approximately constant.

As in the first embodiment, when the ratio between the width of the first inclined surface 31 and the width from the second inclined surface 32 to the third inclined surface 33 is the same in the entire region of the exit surface 2b, the ratio of the reflection width in the first prism portion 3, that is, the reflectance R, is constant. In other words, the amount of the incident light _L2 decreases at a constant rate as the number of reflections increases due to light guiding. For example, when the reflectance R=0.6 and the amount of the first incident light _L21 is 100%, the amount of the first reflected light on the exit surface 2b is 100×0.6=60%, and the amount of the remaining exit light _L3 is 100−60=40%. Next, the amount of the second reflected light on the exit surface 2b is 60×0.6=36%, and the amount of the remaining exit light _L3 is 60−36=24%. The amount of light reflected for the third time on the exit surface 2b is 36×0.6=21.6%, and the amount of light of the remaining exit light _L3 is 36−21.6=14.4%. In this manner, when the ratio of the reflection width on the exit surface 2b is constant, the amount of light of the exit light _L3 decreases as the number of reflections increases, such as 40% for the first exit light _L3 , 24% for the second exit light _L3 , and 14.4% for the third exit light _L3 . For this reason, the farther the position of the display viewing area from the entrance surface 2a, the darker it appears to the user.

In contrast, in this embodiment, the exit surface 2b is composed of multiple regions with different reflection width ratios, and the reflectance R differs for each region. For example, the exit surface 2b is configured so that the reflectance R of the first region 2ba is 2/3, the reflectance R of the second region 2bb is 1/2, and the reflectance R of the third region 2bc is 0.

Hereinafter, as shown in FIG. 9, the emitted light _L3 emitted from the first region 2ba will be referred to as the "first emitted light _L31 ", the emitted light from the second region 2bb will be referred to as the "second emitted light _L32 ", and the light emitted from the third region 2bc will be referred to as the "third emitted light _L33 ".

In this case, when the amount of light of the first incident light _L21 is 100%, the amount of light of the reflected light in the first region 2ba is 100×2/3≒67%, and the amount of light of the first emitted light _L31 is 100-67≒33%. In addition, the amount of light of the reflected light in the second region 2bb is 67×1/2≒34%, the amount of light of the second emitted light _L32 is 67-34≒33%, and since the third incident light _L23 is all emitted in the third region 2bc, the amount of light of the third emitted light _L33 is about 33%. In this way, by configuring the emission surface 2b with a plurality of regions with different reflection width ratios, i.e., reflectances R, the amounts of the emitted lights _L31 to _L33 can be averaged to be approximately the same, and uneven brightness in the display viewing area is reduced.

In the above, a case where the emission surface 2b is composed of three regions 2ba to 2bc has been described as a representative example, but this is not limited thereto, and the emission surface 2b may be composed of multiple regions, and may include two regions or four or more regions.

For example, when the maximum number of reflections of the incident light _L2 on the reflecting surface 2c is m times (m: a natural number equal to or greater than 1), the exit surface 2b is composed of m+1 regions. In this case, the regions are arranged in order from the entrance surface 2a to the first region, the second region, ..., the (m+1)th region, and the ratio of the reflection width becomes smaller from the first region toward the (m+1)th region, and becomes zero in the (m+1)th region. For example, when the exit surface 2b is composed of four regions, the reflectance R in each region may be 3/4 in the first region, 2/3 in the second region, 1/2 in the third region, and 0 in the fourth region. Then, in the case of the emergent surface 2b divided into four, the amount of emergent light _L3 in each region is 100×(1-3/4)=25% in the first region, 75×(1-2/3)=25% in the second region, 50×(1-1/2)=25% in the third region, and the remaining 25% in the fourth region. In this way, when the emergent surface 2b is composed of m+1 regions, the relationship of P _ax /(P _ax +P _bx ) of the xth region is expressed as P _ax /(P _ax +P _bx )=(m+1-x)/(m+2-x) so that the amount of emergent light _L3 in each region becomes uniform. Note that x is an integer between 1 and m, and the reflectance in the m+1 region is 0.

In the first to (m+1)th regions, the reflection widths are Pa1 to Pa(m+1) and the emission widths are Pb1 to Pb(m+1), and the optical member 1 satisfies the following formula (9).

Pa1/Pb1>Pa2/Pb2> ... >Pam/Pbm> Pa(m+1)/Pb(m+1) ... (9)
Moreover, the first prism portions 3 are configured with inclined surfaces of the same angle, except for the region closest to the terminal end face 2d that does not have the first inclined surface 31, and may have the same width and height in each region, or may have different widths and heights. Moreover, in the first region to the mth region, the reflection widths Pa1 to Pam and the emission widths Pb1 to Pbm are preferably set to values within a predetermined range centered on a constant value expressed by the following formulas 10 to 13, where k1 to km are the number of prism portions 3 in each region.

これにより、射出面２ｂにおける反射幅と射出幅との比率が一定とされた周期構造に起因するモアレ発生を抑制することができる。さらには、領域毎に構造の周期が異なるため、各領域内の反射幅と射出幅との比率が一定値である場合でもモアレの発生を抑制することができる。

This makes it possible to suppress the occurrence of moire caused by a periodic structure in which the ratio of the reflection width to the emission width on the emission surface 2b is constant. Furthermore, since the period of the structure differs for each region, the occurrence of moire can be suppressed even if the ratio of the reflection width to the emission width in each region is a constant value.

In addition to the same effects as the first embodiment, the optical element 1 of this embodiment has the effect of averaging the amount of light emitted from the emission surface 2b, ensuring brightness. In addition, when the reflection width and emission width in each region of the emission surface 2b are within a predetermined range centered on a fixed value, the effect of suppressing the occurrence of moire is also obtained.

(First Modification of the Second Embodiment)
10, the optical member 1 may be configured such that the width of the reflecting portion 41 in the light guide direction D1 is Lc, and Lc in the second prism portion 4 varies partially or entirely depending on the location. In other words, the optical member 1 may be configured as a so-called random surface in which the value of Lc in the reflecting surface 2c is random. This makes the reflection pattern of the second incident light _L22 on the reflecting surface 2c no longer constant and makes the incidence pattern of the third incident light _L23 into the second region 2bb and the third region 2bc random, thereby suppressing the occurrence of moire.

This modified example also provides the same effect as the second embodiment, and also provides the effect of suppressing the occurrence of moire in the optical element 1. Note that in this modified example, even if the reflection width and the emission width are constant in each region of the emission surface 2b, the occurrence of moire can be suppressed because the reflection surface 2c is a random surface.

(Second Modification of the Second Embodiment)
The optical member 1 may have a configuration in which the reflecting surface 2c is one flat surface 2ca, as shown in Fig. 11, for example. In this case, the first prism portion 3 on the exit surface 2b has a configuration in which the first inclined surface 31 is parallel to the flat surface 2ca. As a result, the optical member 1 has a configuration in which the reflected light from the first region 2ba and the second region 2bb, i.e., the second incident light _L22 , is reflected by the flat surface 2ca and directed toward the exit surface 2b, as shown in Fig. 12. In addition, the optical member 1 has a configuration in which the gap between the third incident light _L23 is suppressed.

13, for example, when the reflecting surface 2c has a configuration including a plurality of second prism portions 4, there are edge portions between adjacent reflecting portions 41 that do not contribute to the reflection of the second incident light _L22 . For this reason, a gap is generated between the third incident light _L23 that is generated by being reflected by different reflecting portions 41.

On the other hand, in this modification, the reflective surface 2c is a uniform flat surface 2ca, so that the gaps between the above-mentioned light rays, i.e., the periodic reflection pattern caused by the prism array of the reflective surface 2c, do not occur, and therefore the occurrence of moire can be suppressed. Also, in this modification, the reflective surface 2c does not have an edge portion that does not contribute to the reflection of the second incident light _L22 , so that the light is not scattered at the edge portion, and the scattered light is not superimposed on the third incident light _L23 . Therefore, the unintended scattered light is not superimposed on the exit light _L3 , and the effect of further improving the visibility of the outside scene in the display viewing zone is obtained.

This modified example also provides the same effects as the second embodiment, and the optical element 1 has the effects of suppressing the occurrence of moire and improving the visibility of the outside scene in the display viewing area.

(Third Modification of the Second Embodiment)
The optical member 1 may have a cavity layer 5 in the vicinity of the exit surface 2b, as shown in FIG.

The cavity layer 5 is, for example, a plate-shaped space containing air. The cavity layer 5 is arranged in a region of the emission surface 2b that is composed of a plurality of first prism parts 3 having a first inclined surface 31, such as the first region 2ba and the second region 2bb. In other words, the cavity layer 5 is arranged in a region of the emission surface 2b other than the region that does not reflect incident light. The reflecting part 41 of the reflecting surface 2c is the first reflecting surface, and the surface of the cavity layer 5 that is located on the opposite side to the first inclined surface 31 is the second reflecting surface 5a that reflects incident light, as shown in FIG. 15, for example. Note that the width of the cavity layer 5 in the light guide direction D1 is appropriately changed in each region to match the width of the adjacent first inclined surface 31 so as not to prevent light from entering the third inclined surface 33.

The second reflecting surface 5a has the same inclination as the reflecting portion 41 (first reflecting surface), i.e., is parallel to the reflecting portion 41. For example, the second reflecting surface 5a is a surface on which the first incident light _L21 and the third incident light _L23 are totally reflected by the air having a lower refractive index than the light guide 2 being present in the hollow layer 5.

In this modified example, the first inclined surface 31 has a light absorbing film 6 formed on its outer surface. The light absorbing film 6 is made of any material that absorbs visible light, such as black paint, and is formed by any method, such as spray coating. This makes it possible to suppress the intrusion of unnecessary external light into the light guide 2 from the exit surface 2b side and the resulting generation of noise and ghost images.

In this modified example, for example, as shown in FIG. 16, the light guide 2 has a base 21 having a reflective surface 2c and a plurality of third prism portions 7 parallel to the reflective surface 2c, and a prism sheet 22 having a plurality of first prism portions 3. The light guide 2 is formed, for example, by bonding the base 21 and the prism sheet 22 together with an optical adhesive (not shown).

The base 21 has, for example, a prism array on the surface opposite the reflecting surface 2c, in which multiple third prism portions 7 are repeatedly arranged. The third prism portion 7 has, for example, a fourth inclined surface 71 parallel to the reflecting portion 41 and an adjacent surface 72 adjacent thereto. The fourth inclined surface 71 is a portion that constitutes part of the inner wall of the cavity layer 5 by attaching the prism sheet 22. In other words, the fourth inclined surface 71 is a portion that becomes the second reflecting surface 5a. The inclination angle of the adjacent surface 72 with respect to the thickness direction D2 is appropriately adjusted so that total reflection of the incident light does not occur.

The prism sheet 22 is configured such that, for example, the surface opposite the emission surface 2b has a plurality of convex portions 221 having a surface parallel to the adjacent surface 72, and a plurality of concave portions 222 adjacent to the convex portions 221 and having a bottom surface parallel to the fourth inclined surface 71. For example, when the base 21 and the prism sheet 22 are bonded together, the convex portions 221 come into contact with the adjacent surface 72. On the other hand, the bottom surface of the concave portions 222 is located away from the fourth inclined surface 71 at this time, thereby forming, for example, a cavity layer 5 of a plate-shaped space.

This modified example also provides the same effect as the second embodiment, and by disposing the light absorbing film 6 on the first inclined surface 31, the optical element 1 is able to suppress the intrusion of unnecessary external light from the exit surface 2b side and to suppress the occurrence of noise and ghost images.

In addition, the optical member 1 may be configured, for example, as shown in FIG. 17, in which a reflective film 8 made of any material with a visible light reflectance of a predetermined value or more (for example, but not limited to, 99% or more) is arranged in place of the hollow layer 5. In this case, the reflective film 8 of the optical member 1 functions as the second reflective surface. Also, the prism sheet 22 is configured to have a reflective film 8 formed by any method such as sputtering in place of the recess 222. In this case, the optical member 1 can be formed by the same method as above, and the same effect as the above modified example can be obtained.

Other Embodiments
Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one, or less than one, are also within the scope and concept of the present disclosure.

(1) For example, the optical member 1 may be configured by combining the first embodiment with any one of the first to third modified examples of the second embodiment, or may be configured by combining the first or second modified example of the second embodiment with the third modified example. In this way, the optical member 1 may be configured by freely combining the respective embodiments and their modified examples within the possible range.

(2) Furthermore, as shown in FIG. 18, for example, the rear surface 2e of the optical member 1 may have two or more surfaces between the ends 2a1 and 2c1, rather than being a single surface connecting the ends 2a1 and 2c1 in a straight line. In this case, it is sufficient that the angle between the imaginary line VL connecting the ends 2a1 and 2c1 in a straight line and the thickness direction D2 is ξ (<φ). Furthermore, the rear surface 2e may be a curved surface. Thus, the shape of the rear surface 2e is arbitrary in each of the above-mentioned embodiments and their modified examples.

(3) It goes without saying that in each of the above embodiments, the elements constituting the embodiment are not necessarily essential, except when expressly stated as essential or when it is clearly considered essential in principle. Furthermore, in each of the above embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiment are mentioned, they are not limited to the specific numbers, except when expressly stated as essential or when it is clearly limited to a specific number in principle. Furthermore, in each of the above embodiments, when the shapes, positional relationships, etc. of the components, etc. are mentioned, they are not limited to the shapes, positional relationships, etc., except when expressly stated as essential or when it is clearly limited to a specific shape, positional relationship, etc. in principle.

2...light guide, 2a...incident surface, 2a1...end of incident surface opposite to the exit surface 2b...exit surface, 2c...reflecting surface, 2c1...end of reflecting surface on the incident surface side 3...first prism portion, 31...first inclined surface, 32...second inclined surface, 33...third inclined surface 4...second prism portion, 41...reflecting portion, 42...adjacent surface D2...thickness direction, Pa1 to Pa(m+1)...width of first inclined surface Pb1 to Pb(m+1)...width from second inclined surface to third inclined surface Td...maximum thickness of incident surface (incident surface height), Ts...distance between exit surface and reflecting surface VL...imaginary straight line connecting end of incident surface and end of reflecting surface

Claims (11)

An optical member that internally reflects and guides external light,
a light guide (2) having an incident surface (2a) on which the external scene light is incident, an exit surface (2b) on which the incident light incident from the incident surface first arrives and which reflects the incident light and exits it to the outside, and a reflection surface (2c) disposed opposite the exit surface and which reflects light of the incident light reflected by the exit surface toward the exit surface;
The exit surface has a plurality of prism portions (3) each composed of a plurality of inclined surfaces (31, 32, 33) having different inclinations,
The optical member has a common inclined surface (41) that is a surface having the same inclination as one of the plurality of inclined surfaces. The optical element according to claim 1, wherein one of the inclined surfaces that emits a portion of the incident light to the outside is defined as an emission section (33), and the emission section is parallel to the incident surface. The plurality of prism portions constituting the exit surface are designated as first prism portions,
2. The optical element according to claim 1, wherein the reflective surface has a plurality of second prism portions (4) each having a reflective portion (41) that is a surface that reflects light of the incident light reflected at the exit surface to the exit surface, and an adjacent surface (42) adjacent to the reflective portion. The optical element according to claim 3, wherein the reflecting portion is parallel to one of the inclined surfaces (31) that reflects the incident light. The refractive index of the light guide is n, one of the inclined surfaces (31) reflects the incident light, and an angle between the normal direction to the reflecting surface and the direction in which the incident light travels is δ,
The optical member according to claim 1 , wherein the one inclined surface and the reflecting surface are inclined so as to satisfy sin δ>1/n. The direction connecting the exit surface and the reflecting surface is defined as a thickness direction (D2), the angle between the incident direction of the external light on the entrance surface and the thickness direction is defined as θ, the angle between the direction in which the light of the incident light proceeds toward the exit surface and the thickness direction is defined as φ, and the angle between the direction in which the light of the incident light proceeds toward the reflecting surface and the thickness direction is defined as ε,
2. The optical member according to claim 1, wherein one of the plurality of inclined surfaces that reflects the incident light and the incident surface are inclined so as to satisfy ε>φ>θ. A direction connecting the exit surface and the reflecting surface is defined as a thickness direction (D2), and an angle between the entrance surface and the thickness direction is defined as ψ.
The optical member according to claim 1 , wherein the incidence surface is inclined so as to satisfy ψ<φ. The optical element according to claim 1, wherein the exit surface has three or more of the inclined surfaces. In the light guide, the direction in which the incident light travels after being reflected by the emission surface and the reflection surface is defined as a light guide direction (D1), one of the multiple inclined surfaces that reflects a portion of the incident light is defined as a first inclined surface (31), a surface adjacent to the first inclined surface is defined as a second inclined surface (32), and a surface that is disposed on the opposite side of the second inclined surface from the first inclined surface and that emits a portion of the incident light to the outside is defined as a third inclined surface (33),
the emission surface has a plurality of regions (2ba to 2bc) having different ratios between a first width (Pa1 to Pa(m+1)) of the first inclined surface in the light guiding direction and a second width (Pb1 to Pb(m+1)) from the second inclined surface to the third inclined surface in the light guiding direction,
The optical member according to claim 8 , wherein the ratio of the first width to the second width of the plurality of regions decreases as the region is positioned farther from the incident surface. A direction connecting the emission surface and the reflection surface is defined as a thickness direction (D2), and a distance from the emission surface to an end (2a1) of the incidence surface opposite to the emission surface is defined as an incidence surface height (Td),
the height of the incident surface is greater than a distance (Ts) between the exit surface and the reflecting surface in the thickness direction,
The angle between the thickness direction and a virtual line (VL) that linearly connects the end and the end (2c1) of the reflecting surface on the side of the incident surface is defined as ξ, and the angle between the thickness direction and the direction in which the light toward the exit surface of the incident light travels is defined as φ.
The optical member according to claim 1 , wherein the light guide satisfies ξ<φ. The reflecting surface is a first reflecting surface, and the light guide has a second reflecting surface (5a, 8) therein that reflects the incident light to the first reflecting surface,
The optical member according to claim 1 , wherein the second reflecting surface is parallel to the same inclined surface of the first reflecting surface.

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