JP2018066799A - Image display device and optical see-through display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small light-weight image display device having both a sufficient pupil size and a sufficient screen size.SOLUTION: An image display device is provided, in which the entire principal rays on a fold-back cross-section including the principal rays of illumination light L0 of a liquid crystal display element 20 and the principal rays of reflected image light L1 satisfy 0<θ<5, where θ represents an incident angle of the principal rays in the fold-back cross-section with respect to a display screen, and 30<φ<47, P/S×L>4, H/P>0.2, S<9, 0.43<D2/D1<2.2 and 4.0<P×T/(D1+D2)<25, where φ represents an angle formed by the normal line on a polarization separation plane of a PBS (polarizing beam splitter) and a the normal line of the display screen; P represents the focal distance of a reflection surface having a power; S represents the focal distance of an illumination optical system; L represents the size of a light source on the fold-back cross-section; H represents the size of the display element on the fold-back cross-section; D1 represents the distance in the principal rays of incident illumination light of the display element, from an exit surface of the illumination optical system to the PBS; D2 represents the distance in the principal rays of incident illumination light of the display element from the PBS to the display element; and T represents the size of the illumination optical system in a direction perpendicular to the optical axis on the fold-back cross-section.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image display device and an optical see-through display. For example, a two-dimensional image of a liquid crystal display (LCD) is projected onto an observer's eye using a holographic optical element (HOE). The present invention relates to a see-through type image display device for displaying and an optical see-through display such as an HMD (head mounted display) equipped with the image display device.

  A head-mounted display (HMD) is required to have high wearability while having high optical performance, from the mounting form of being mounted on the head. Here, the wearability means that the wearer does not feel uncomfortable, and is light and difficult to shift. Therefore, not only the HMD but also a display of a type that is worn on a part of the body (neck, shoulder, arm, etc.) requires high wearability. A see-through type HMD having components such as a reflective liquid crystal display element, a light guide prism, a flat type PBS (polarizing beam splitter), an illumination optical system, an LED (light emitting diode) light source, It is proposed in Patent Documents 1 to 4.

  The image display device described in Patent Document 1 includes a light guide prism that reflects image light twice, a reflective liquid crystal display element, PBS, an illumination optical system, and an LED light source. The image display device described in Patent Document 2 includes a light guide prism that reflects image light twice and a reflective liquid crystal display element. The image display device described in Patent Document 3 includes a light guide prism that reflects image light three times, a flat PBS, and an illumination optical system. The light guide prism has a reflective surface with power 1. Only the surface is provided, and the planar PBS is joined to the prism surface. The image display device described in Patent Document 4 includes a light guide prism that reflects image light twice, a reflective liquid crystal display element, an illumination optical system, and an LED light source.

Japanese Patent Application No. 2009-97489 JP 2000-352689 A WO2014156602 A1 JP 2002-55304 A

  However, the image display devices described in Patent Documents 1 to 4 have a large incident angle of all principal rays with respect to the image display surface in the folded cross section of the reflective liquid crystal display element on the image display surface. It is getting bigger. When it is attempted to reduce the size of the entire image display device, it is difficult to ensure sufficient pupil size and screen size.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a small and lightweight image display device having a sufficiently large pupil size and screen size, and to be easily mounted with the image display device. It is to provide an optical see-through display.

In order to achieve the above object, an image display apparatus according to a first invention includes a light source that emits illumination light, an illumination optical system that collimates incident light, a planar polarization beam splitter that performs polarization separation of incident light, A reflective liquid crystal display element that performs spatial modulation for image display with respect to incident light, and a prism that causes incident light incident from the incident surface to exit from the exit surface after being reflected twice,
The prism has a reflective surface with power,
Illumination light from the light source is collimated by the illumination optical system, the collimated illumination light is reflected by the polarization beam splitter, and the reflected illumination light is spatially modulated by the liquid crystal display element to generate image light. The image light is incident on the prism from the incident surface after being transmitted by the polarization beam splitter, and the image light is reflected by the reflecting surface having the power after being reflected by the emitting surface. An image display device that emits out of the prism and enters the pupil of an observer,
When a plane including the chief ray of illumination light just before incidence on the center of the screen of the liquid crystal display element and the chief ray of image light just after reflection is a folded section,
The following conditional expression (1) is satisfied for all principal rays in the folded section:
The following conditional expressions (2) to (7) are satisfied.
0 <θ <5 (1)
30 <φ <47 (2)
P / S × L> 4 (3)
H / P> 0.2 (4)
S <9 (5)
0.43 <D2 / D1 <2.2 (6)
4.0 <P × T / (D1 + D2) <25 (7)
However,
θ: the incident angle (degrees) of the principal ray with respect to the screen of the liquid crystal display element in the folded section,
φ: Angle (degrees) between the normal of the polarization separation plane of the polarizing beam splitter and the normal of the screen of the liquid crystal display element,
P: focal length (mm) of the reflecting surface with power,
S: Focal length of illumination optical system (mm),
L: the size (mm) of the light source in the folded section,
H: size of liquid crystal display element in folded section (mm),
D1: distance (mm) from the exit surface of the illumination optical system to the polarization beam splitter in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
D2: distance (mm) from the polarizing beam splitter to the liquid crystal display element in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
T: the size (mm) of the illumination optical system that occupies the folded section in the direction perpendicular to the optical axis of the illumination optical system,
It is.

An image display device according to a second aspect of the invention is characterized in that, in the first aspect of the invention, the following conditional expression (7a) is satisfied.
4.0 <P × T / (D1 + D2) <13 (7a)
However,
P: focal length (mm) of the reflecting surface with power,
T: the size (mm) of the illumination optical system that occupies the folded section in the direction perpendicular to the optical axis of the illumination optical system,
D1: distance (mm) from the exit surface of the illumination optical system to the polarization beam splitter in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
D2: distance (mm) from the polarizing beam splitter to the liquid crystal display element in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
It is.

  According to a third aspect of the present invention, there is provided the image display device according to the first or second aspect, wherein the prism has only one reflecting surface having power, and the polarizing beam splitter is an incident surface of the prism. It is characterized by being joined to.

According to a fourth aspect of the present invention, there is provided the image display device according to any one of the first to third aspects, wherein the following conditional expression (8) is satisfied.
18 <K <30 (8)
However,
K: optical path length (mm) from the exit surface of the prism to the exit pupil in the optical path of the principal ray exiting from the center of the screen of the liquid crystal display element;
It is.

  The image display device of a fifth invention is characterized in that, in any one of the first to fourth inventions, the reflective surface having power is a hologram surface.

  According to a sixth aspect of the present invention, in the fifth aspect, the hologram surface has a shape having a curvature only in a direction perpendicular to an eccentric direction.

An image display device according to a seventh invention is characterized in that, in the fifth or sixth invention, the following conditional expression (9) is satisfied.
83 <M <120 (9)
However,
M: Angle (degrees) between the normal of the hologram surface and the lower marginal ray of the screen angle of view of the liquid crystal display element,
It is.

An image display apparatus according to an eighth invention is characterized in that, in any one of the first to seventh inventions, the following conditional expression (10) is satisfied.
L1 <2.0 (10)
However,
L1: Physical optical path length (mm) from the reflection position on the exit surface of the prism to the reflective surface with power in the optical path of the lower marginal ray of the lower screen angle of view of the liquid crystal display element;
It is.

An image display device according to a ninth invention is characterized in that, in any one of the first to eighth inventions, the following conditional expression (11) is satisfied.
L2 <5.0 (11)
However,
L2: physical optical path length (mm) from the incident surface of the prism to the reflection position on the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is.

  According to a tenth aspect of the present invention, in any one of the first to ninth aspects, an LED light source is arranged as the light source in the vicinity of a focal position of the illumination optical system.

  According to an eleventh aspect of the present invention, there is provided the image display device according to any one of the first to tenth aspects, wherein the illumination optical system includes a Fresnel lens that is a single lens.

  The image display device according to a twelfth aspect of the present invention is the image display device according to any one of the first to eleventh aspects, wherein the illumination optical system includes a diffuser plate that is diffusible in a direction perpendicular to the folded cross section. As described above, independent LED light sources corresponding to the three primary colors RGB are arranged in a direction perpendicular to the folded cross section.

  An image display device according to a thirteenth aspect of the present invention is the image display device according to any one of the first to twelfth aspects, wherein the second display surface is bonded to the reflective surface having the power so as to have a prism surface parallel to the exit surface. The prism is further provided.

An image display device according to a fourteenth invention is characterized in that, in any one of the first to thirteenth inventions, the following conditional expression (12) is satisfied.
0.65 <D / B <1.0 (12)
However,
B: thickness of second prism (mm),
D: distance (mm) from the reflecting surface having the power of the prism to the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is.

An image display device according to a fifteenth aspect of the invention is characterized in that, in any one of the first to fourteenth aspects, the following conditional expression (12a) is satisfied.
0.8 <D / B <0.9 (12a)
However,
B: thickness of second prism (mm),
D: distance (mm) from the reflecting surface having the power of the prism to the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is.

  An optical see-through display according to a sixteenth aspect of the present invention is equipped with the image display device according to any one of the first to fifteenth aspects of the present invention, so that the display image of the liquid crystal display element is seen through to the observer's eye on the hologram surface. It is characterized by having a function of projecting and displaying.

  An optical see-through display according to a seventeenth aspect is characterized in that, in the sixteenth aspect, a support member is provided for supporting the image display device so that the hologram surface is positioned in front of an observer's eye.

  According to the present invention, it is possible to realize a small and lightweight image display device having a sufficiently large pupil size and screen size, and an optical see-through display having the wearability.

1 is a schematic cross-sectional view schematically showing an embodiment (Examples 1 and 2) of an image display device. The enlarged view which shows the optical structure before the prism incidence in the image display apparatus of FIG. The enlarged view which shows the optical structure after the prism incidence in the image display apparatus of FIG. The perspective view which shows the spectacles type head mounted display provided with the image display apparatus of FIG. Sectional drawing for demonstrating application of conditional expression (7) in an image display apparatus. The optical path figure for demonstrating application of conditional expression (9) in an image display apparatus. Sectional drawing which shows the state which the 2nd prism maximized regarding conditional expression (12) in an image display apparatus. Sectional drawing which shows the state which the 2nd prism minimized regarding the conditional expression (12) in an image display apparatus. 1 is an optical path diagram illustrating an optical configuration of first and second embodiments of an image display device. FIG. 6 is a schematic cross-sectional view schematically showing Example 3 of the image display device. FIG. 6 is a schematic cross-sectional view schematically showing Example 4 of the image display device.

  Hereinafter, an image display device, an optical see-through display, and the like according to embodiments of the present invention will be described. Note that the same or corresponding parts in the embodiments, examples, and the like are denoted by the same reference numerals, and redundant description is omitted as appropriate.

  An image display device according to an embodiment of the present invention includes a light source that emits illumination light, an illumination optical system that collimates incident light, a planar polarization beam splitter that performs polarization separation of incident light, and an image for incident light. It has a reflective liquid crystal display element that performs spatial modulation for display, and a prism that emits incident light incident from an incident surface after being reflected twice. The prism has a reflective surface with power (power: an amount defined by the reciprocal of the focal length), and the illumination light from the light source is collimated by the illumination optical system, and the collimated illumination is obtained. Light is reflected by the polarization beam splitter, and the reflected illumination light is spatially modulated by the liquid crystal display element to generate image light. The image light is transmitted through the polarization beam splitter and then enters the prism from the incident surface. Then, the image light is reflected by the exit surface, then reflected by the reflective surface having power, exits the prism from the exit surface, and enters the observer's pupil.

Further, the image display device has a folded section when a plane including a principal ray of illumination light immediately before incidence with respect to the center of the screen of the liquid crystal display element and a principal ray of image light just after reflection is a folded section. It is characterized in that the following conditional expression (1) is satisfied for all the chief rays in and the following conditional expressions (2) to (7) are satisfied.
0 <θ <5 (1)
30 <φ <47 (2)
P / S × L> 4 (3)
H / P> 0.2 (4)
S <9 (5)
0.43 <D2 / D1 <2.2 (6)
4.0 <P × T / (D1 + D2) <25 (7)
However,
θ: the incident angle (degrees) of the principal ray with respect to the screen of the liquid crystal display element in the folded section,
φ: Angle (degrees) between the normal of the polarization separation plane of the polarizing beam splitter and the normal of the screen of the liquid crystal display element,
P: focal length (mm) of the reflecting surface with power,
S: Focal length of illumination optical system (mm),
L: the size (mm) of the light source in the folded section,
H: size of liquid crystal display element in folded section (mm),
D1: distance (mm) from the exit surface of the illumination optical system to the polarization beam splitter in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
D2: distance (mm) from the polarizing beam splitter to the liquid crystal display element in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
T: the size (mm) of the illumination optical system that occupies the folded section in the direction perpendicular to the optical axis of the illumination optical system,
It is.

  Examples of the light source for illumination include an LED light source, a laser light source, and an organic EL (Organic Electro-Luminescence) light source. By collimating the illumination light from the light source with the illumination optical system, the illumination light emitted by the light source can be efficiently delivered to the observer's pupil. In addition to spatially modulating the illumination light, a reflective liquid crystal display element is used for miniaturization by turning back the light. A planar polarization beam splitter (planar PBS) is used to define the polarized light incident on the reflective liquid crystal display element in a small space and to selectively transmit the modulated light. By utilizing the two polarization separation functions of generating polarized light by reflection and selecting polarized light by transmission, it is possible to reduce the size of the optical configuration. In the prism, reflection is performed twice between the incidence and the emission. By configuring the light guide optical system reflecting twice with the prism, the reflective liquid crystal display element, which is a large component, can be disposed on the opposite side of the observer's eye. As a result, it is possible to avoid interference between the liquid crystal display element and the forehead or glasses of the observer.

  With respect to the arrangement configuration and optical configuration of each of the above-mentioned parts, an image can be obtained while ensuring a sufficiently large pupil size and screen size by satisfying the conditional expressions (1) to (7) as described below. The display device can be reduced in weight and size, and by including the display device, it is possible to realize an optical see-through display such as an HMD with good wearability.

  By satisfying conditional expression (1) and conditional expression (2), it is possible to reduce the space in the folded section and reduce the weight by reducing the size of the parts. If it is telecentric with respect to the liquid crystal display element and the angle of the light ray with respect to the screen is 90 ° reflection, the optical system (planar PBS or the like) becomes minimum, so that conditional expression (1) is satisfied. The condition of the reflected reflection is not greatly deviated. That is, conditional expression (1) means that the principal rays at the time of incidence and reflection at the screen of the reflective liquid crystal display element substantially coincide. Similarly, the conditional expression (2) means that the polarization separation plane of the flat PBS and the screen of the liquid crystal display element form approximately 45 °. If the conditional expression (2) is satisfied, the area of the planar PBS is reduced, and thus it is possible to reduce the weight and size. Also, if the lower limit of conditional expression (2) is exceeded, the illumination optical system is easily established, and if the lower limit of conditional expression (2) is not reached, the light source should not interfere with the observer's forehead or eyes. Becomes easier.

  Conditional expression (3) indicates that the focal length of the reflecting surface with power (focal length due to diffraction action in the case of a hologram surface) P, the focal length S of the illumination optical system, and the size L of the light source in the folded section. Stipulates the relationship. Since the size of a general human pupil is 4 mm, conditional expression (3) defines that the observation range (exit pupil) is larger than that. That is, by satisfying conditional expression (3), it is possible to secure a sufficiently large pupil size so that the display image can be seen well (increasing pupil size).

  Conditional expression (4) defines the relationship between the size H of the liquid crystal display element in the folded section and the focal length (focal length due to diffractive action in the case of a hologram surface) P of the reflecting surface having power. Yes. Since this is a condition setting corresponding to the angle of view in the folded section direction, satisfying conditional expression (4) can ensure a screen size for providing a large image to the observer (large screen size). ).

  Conditional expression (5) defines the power of the illumination optical system. By satisfying this conditional expression (5), it is possible to easily avoid interference between the light source and the forehead of the observer or glasses while reducing the weight of the parts.

  Conditional expression (6) indicates that the ratio of the distance D1 from the exit surface of the illumination optical system to the flat type PBS and the distance D2 from the flat type PBS to the reflective liquid crystal display element is incident on the center of the screen of the liquid crystal display element. It is defined based on the principal ray of the luminous flux. Since illumination light and image light are incident on the planar PBS on the prism, it is necessary to balance the weight of the illumination optical system and the liquid crystal display element, and it is important to determine the center of gravity of the illumination optical system appropriately. . Conditional expression (6) is a condition setting for maintaining the center of gravity of the entire optical system in the vicinity of the prism. When this conditional expression (6) is satisfied, a display such as an HMD equipped with an image display device is mounted. Wearing misalignment can be prevented (high wearability). If the distance D2 is too long and exceeds the upper limit of the conditional expression (6), the liquid crystal display element is moved far away, so that the center of gravity of the entire optical system moves forward, and a display such as an HMD is easily displaced. When the distance D1 is too long and falls below the lower limit of the conditional expression (6), the center of gravity of the entire optical system moves upward, and a display such as an HMD is easily displaced.

  Conditional expression (7) is a condition setting for realizing high wearability in which wearing shift is unlikely to occur while securing the pupil size. The lower limit and upper limit of the condition range will be described below. However, as an example of the constituent elements of the image display device, as shown in FIG. 5, assuming a light source ES, an illumination optical system E1, a liquid crystal screen EG, and a reflective surface E2 with power, the illumination light L0 from the light source ES is a liquid crystal. It is assumed that the image light L1 obtained by being modulated by the screen EG is incident on the pupil of the observer eye EY.

  When attention is paid to the light at the center of the liquid crystal screen EG, the marginal ray emitted from the liquid crystal screen EG at an angle ψ becomes substantially parallel light on the reflecting surface E2 having power and enters the pupil of the observer's eye EY. From the relationship between the focal length P of the reflecting surface having power and the size of the pupil, the formula (F1): tan ψ = (pupil size) / 2P is established. Next, paying attention to the illumination optical system E1, the incident angle of light with respect to the center of the liquid crystal screen EG is the angle ψ as described above. The size T of the illumination optical system E1 that occupies a direction perpendicular to the optical axis AX of the illumination optical system in the folded section (corresponding to the plane of the drawing) is such that the marginal ray at the center of the liquid crystal screen EG enters the illumination optical system E1 Therefore, from the relationship between the size T of the illumination optical system E1 and the distance D1 + D2, the equation (F2): tanψ <T / {2 (D1 + D2)} holds.

  From the above two formulas (F1) and (F2), the condition of the illumination optical system E1 for securing the exit pupil at a size of the human pupil: 4 mm or more is the formula (F3) representing the lower limit of the conditional formula (7). ): It is defined by 4.0 <P × T / (D1 + D2). The lower limit of conditional expression (7) means that the light at the center of the liquid crystal screen EG reaches the pupil of the observer's eye EY with a sufficiently large exit pupil, as in conditional expression (3). By satisfying 7) on the lower limit side, it is possible to secure a sufficiently large pupil size so that the display image can be seen well (increasing the pupil size).

  When comparing the size T of the illumination optical system E1 and the size H of the liquid crystal screen EG, if the liquid crystal screen EG is too large, the center of gravity of the entire optical system is shifted forward, and the display such as the HMD is easily shifted. The upper limit of conditional expression (7) defines a condition for preventing the center of gravity from shifting to the observer's eye EY side because the diameter of the illumination optical system E1 becomes too large. From expression (F4): T <4H It is calculated. When the size of the illumination optical system E1 satisfies the formula (F4): T <4H, the center of gravity is not excessively shifted to the observer eye EY side, and high wearability can be ensured. From this, an expression (F5) representing the upper limit of the conditional expression (7): P × T / (D1 + D2) <25 is defined.

  In the above conditional expressions (3) to (7), a plurality of parameters coexist and are correlated with each other. Therefore, by satisfying these conditional expressions (3) to (7) at the same time, an image display device having a sufficient pupil size and screen size while being downsized can be obtained. In addition, the image display apparatus having the above-described characteristic configuration can be reduced in size and weight while having a sufficiently large pupil size and screen size. By providing the image display device, an optical see-through display (for example, a head-mounted display) with good wearability can be realized. The conditions for obtaining such effects in a well-balanced manner and achieving further weight reduction, miniaturization, high performance, etc. will be described below.

It is desirable that the following conditional expression (7a) is satisfied.
4.0 <P × T / (D1 + D2) <13 (7a)
This conditional expression (7a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (7). Therefore, the above effect can be further increased preferably by satisfying conditional expression (7a).

  It is desirable that the power reflecting surface provided on the prism is only one surface, and the polarizing beam splitter is joined to the incident surface of the prism. Since the polarization beam splitter and the prism are integrated into one component by bonding, an assembly error is reduced and a gap is not required, which contributes to downsizing of the entire image display apparatus.

It is desirable to satisfy the following conditional expression (8).
18 <K <30 (8)
However,
K: optical path length (mm) from the exit surface of the prism to the exit pupil in the optical path of the principal ray exiting from the center of the screen of the liquid crystal display element;
It is.

  Conditional expression (8) prescribes conditions under which interference with the observer's forehead and glasses can be easily avoided without increasing the size of the image display device. If the value is lower than the upper limit of the conditional expression (8), it is possible to prevent the prism from being easily displaced away from the observer's forehead and glasses, and to effectively suppress the enlargement of the image display device. The spectacle wearing distance can be assumed to be 12 mm + lens thickness 3 mm + margin 3 mm from the observer's eye. Therefore, if the lower limit of conditional expression (8) is exceeded, even a person wearing glasses can easily and properly observe the display image without hitting the glasses against the image display device.

  The reflective surface having power is preferably a hologram surface. See-through property can be obtained by configuring a powerful reflecting surface with a hologram optical element. Therefore, an optical see-through display can be realized by using a hologram surface as a reflecting surface with power for a prism.

  It is desirable that the hologram surface has a shape having a curvature only in a direction perpendicular to the eccentric direction. Since the hologram surface can have power even on a flat surface, aberration correction or the like can be performed using a shape having a curvature only in one direction. In addition, since there is no curvature in the thickness direction of the prism, it is effective for downsizing the image display device.

It is desirable to satisfy the following conditional expression (9).
83 <M <120 (9)
However,
M: Angle (degrees) between the normal of the hologram surface and the lower marginal ray of the screen angle of view of the liquid crystal display element,
It is.

  Conditional expression (9) prescribes a preferable condition range for reducing the size of the upper front portion of the prism (the portion of the upper external side as viewed from the observer) and preventing light from exiting the prism. . FIG. 6 shows the hologram surface 11c and the lower marginal ray LM in the state where the conditional expression (9) is satisfied (NL: normal of the hologram surface, 11b: exit surface of the prism). 6A shows a state where the angle M is about 90 °, FIG. 6B shows a state α1 where the angle M is close to 120 °, and FIG. 6C shows a state α2 where the angle M is close to 83 °. As can be seen from FIG. 6B, when the upper limit of the conditional expression (9) is exceeded, the light tends to be emitted outside the prism. As can be seen from FIG. 6C, when the lower limit of conditional expression (9) is not reached, the upper front portion of the prism tends to be enlarged.

It is desirable to satisfy the following conditional expression (10). This conditional expression (10) defines a preferable condition range for reducing the size of the lower part of the prism (the lower part as viewed from the observer).
L1 <2.0 (10)
However,
L1: Physical optical path length (mm) from the reflection position on the exit surface of the prism to the reflective surface with power in the optical path of the lower marginal ray of the lower screen angle of view of the liquid crystal display element;
It is.

It is desirable to satisfy the following conditional expression (11). Conditional expression (11) defines a preferable condition range for reducing the size of the upper rear side portion of the prism (upper observer eye side portion as viewed from the observer).
L2 <5.0 (11)
However,
L2: physical optical path length (mm) from the incident surface of the prism to the reflection position on the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is.

  It is desirable that an LED light source is disposed as the light source in the vicinity of the focal position of the illumination optical system. By arranging the LED light source in the vicinity of the focal position of the illumination optical system, it is possible to collimate the illumination light from the LED light source and to ensure the brightness of the liquid crystal screen appropriately.

  It is desirable that the illumination optical system has a Fresnel lens that is a single lens. By configuring the illumination optical system with a single lens Fresnel lens, it is possible to make the illumination optical system thin while collimating the illumination light from the LED light source.

  The illumination optical system has a diffuser plate that is diffusible in a direction perpendicular to the folded section, and an independent LED light source corresponding to the three primary colors RGB is arranged in the direction perpendicular to the folded section as the light source. It is desirable that By arranging the RGB independent LED light sources in a direction perpendicular to the folded cross section and diffusing the illumination light with the diffusion plate in that direction, the illumination light can be mixed evenly and color unevenness can be eliminated.

  It is desirable to further have a second prism bonded to the reflective surface having power so as to have a prism surface parallel to the exit surface. Adhering the second prism so that the opposite surface of the prism is parallel to the exit surface of the prism, the two surfaces of both prisms are parallel to each other, ensuring good see-through performance. It becomes possible to do.

It is desirable to satisfy the following conditional expression (12).
0.65 <D / B <1.0 (12)
However,
B: thickness of second prism (mm),
D: distance (mm) from the reflecting surface having the power of the prism to the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is.

  Conditional expression (12) defines a preferable range of conditions for ensuring both an upper field of view and a reduction in the thickness of the prism. If the upper limit of conditional expression (12) is exceeded, bonding is performed so as to cover only the light beam region using the second prism, and the weight tends to be reduced while it is difficult to ensure the upper field of view. Become. Even if both sides of the prism are kept parallel by adhering the second prism, if it falls below the lower limit of the conditional expression (12), it will be adhering so as to cover everything on the hologram surface extension line with the second prism. Therefore, the upper field of view can be secured, but the prism becomes thick and the weight tends to increase.

It is desirable that the following conditional expression (12a) is satisfied.
0.8 <D / B <0.9 (12a)
This conditional expression (12a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (12). Therefore, preferably, the above effect can be further increased by satisfying conditional expression (12a).

  FIG. 1 is a schematic cross-sectional view showing a more specific example of an optical configuration in an embodiment of an image display device. FIG. 2 is an enlarged view of the optical configuration before incidence of the prism, and shows the optical configuration after incidence of the prism. 3 is enlarged. In addition, each parameter of conditional expression (1)-(12) mentioned above in FIG.2, FIG.3 is shown.

  An image display device 1 shown in FIG. 1 includes an LED light source 21 that emits illumination light L0, a diffusion plate 22 that diffuses illumination light L0 from the LED light source 21, a Fresnel lens 23 that collimates the illumination light L0, and incident light. It has a planar PBS 24 that performs polarization separation, a reflective liquid crystal display element 20 that performs spatial modulation for image display on the illumination light L0, and an optical device 10 that functions as an eyepiece optical system. FIG. 1 shows an optical path from the LED light source 21 to the exit pupil EP in the image display device 1.

  The LED light source 21 is composed of independent LEDs corresponding to the three primary colors RGB that emit light in three wavelength bands (emission peak wavelengths are, for example, 450 nm, 532 nm, and 640 nm). That is, the LED light sources 21 are arranged independently in RGB in the vertical direction (X direction) with respect to the folded section (corresponding to the plane of the drawing). For this reason, it is necessary to diffuse the illumination light L0 from the LED light source 21.

  As a part of the illumination optical system, the diffuser plate 22 diffuses the illumination light L0 from the LED light source 21, thereby uniformly mixing the illumination light L0 to eliminate color unevenness, and the degree of diffusion varies depending on the direction. ing. That is, the unidirectional diffuser plate has a diffusing action only in the vertical direction (X direction) with respect to the folded section, and the direction having the diffusing action is the same as the arrangement direction of the independent LED light sources 21 corresponding to RGB. The illumination light L0 from the LED light source 21 is diffused by passing through the diffusion plate 22, and then collimated by a Fresnel lens 23 that forms part of the illumination optical system. The collimated illumination light L0 is reflected by the flat type PBS 24 so that the polarization direction is aligned and then enters the liquid crystal display element 20.

  As a condition setting related to the conditional expression (5), it is desirable that the focal length of the Fresnel lens 23 forming a part of the illumination optical system is less than 9 mm. This is because parts such as the LED light source 21 interfere with the observer's forehead and eyes when the focal length is 9 mm or more. The focal length of the Fresnel lens 23 in Example 1 to be described later is 7.2 mm. Further, the LED light source 21 is arranged in the vicinity of the focal position of the Fresnel lens 23 in order to collimate the illumination light L0 emitted from the LED light source 21.

  The angle θ in the conditional expression (1) is shown in FIG. 2B, and the angle φ in the conditional expression (2) is shown in FIG. FIG. 2B shows an enlarged incident light path of the principal ray with respect to the screen 20a of the liquid crystal display element 20 in the folded section in the optical configuration before incidence of the prism shown in FIG. In Example 1, which will be described later, the incident angle θ to the liquid crystal display element 20 is 0.35 degrees for the principal ray at the center of the screen 20a, 0.50 degrees for the principal ray below the screen, and 0. It is 28 degrees. Further, an angle φ formed between the normal line of the planar PBS 24 and the normal line of the screen 20a of the liquid crystal display element 20 is 44 degrees. Therefore, the conditional expression (1) for reducing the space for folding is satisfied, and the conditional expression (2) is satisfied on the lower limit side in order to establish the illumination optical system. Conditional expression (2) is satisfied on the upper limit side so as not to interfere with the forehead and eyes.

  The liquid crystal display element 20 is arranged so that light that is incident substantially perpendicularly from the planar PBS 24 is reflected substantially perpendicularly toward the planar PBS 24. This facilitates optical design that increases the resolution compared to a configuration in which the illumination light L0 is incident on the screen 20a of the liquid crystal display element 20 at a large incident angle. The liquid crystal display element 20 generates image light L1 by performing spatial modulation for image display on the illumination light L0 according to the image signal. At this time, the image light L1 corresponding to the image signal ON is converted into light having a polarization direction orthogonal to that of the illumination light L0 incident on the liquid crystal display element 20, and is thus transmitted through the planar PBS 24 and the optical device. 10 is incident on the inside. On the other hand, the image light L1 corresponding to the image signal OFF is emitted by the liquid crystal display element 20 without changing the polarization direction, and thus is blocked by the flat PBS 24 and does not enter the optical device 10.

  The optical device 10 includes transparent first and second prisms 11 and 12; a hologram optical element 13 and the like, and the flat PBS 24 is attached to the incident surface 11a of the first prism 11. By integrating the flat PBS 24 and the incident surface 11a of the first prism 11, the optical configuration can be reduced. The optical device 10 has a structure having a hologram optical element 13 between the first prism 11 and the second prism 12. The hologram optical element 13 is affixed to the first prism 11, and the first prism 11 and the second prism 12 are bonded by an adhesive 14 provided between the first and second prisms 11 and 12. The hologram optical element 13 is bonded so as to sandwich it. That is, the first prism 11 and the second prism 12 are joined by the adhesive 14 provided between the first prism 11 and the hologram optical element 13 and the second prism 12. Yes. Since the hologram optical element 13 is provided on the joint surfaces of the prisms 11 and 12 which are transparent substrates, the see-through property (combiner function) of the external image through the joint surface is ensured.

  The optical device 10 magnifies the display image IM so that the display image IM of the liquid crystal display element 20 overlaps the external image via the hologram optical element 13 between the joined first and second prisms 11 and 12. As an eyepiece optical system for projecting and displaying on the observer eye EY. Therefore, the hologram optical element 13 is desirably a volume phase type reflection hologram. Since the volume phase type reflection hologram has a high light transmittance of the external field image, if the volume phase type reflection hologram is used as the hologram optical element 13, the observer can clearly observe the external image as well as the display image IM. Is possible. Note that it is preferable that the RGB diffraction wavelengths of the hologram optical element 13 correspond to the wavelengths of the RGB image light L1 (the emission wavelength of the LED light source 21).

  The optical device 10 has a non-axisymmetric (non-rotationally symmetric) positive optical power in the hologram optical element 13. By having the hologram surface 11c composed of the hologram optical element 13 as a reflective surface with power in the first prism 11, it becomes possible to guide the image light L1 from the liquid crystal display element 20 to the exit pupil EP. In addition, since the hologram surface 11c has a shape having a curvature only in a direction perpendicular to the eccentric direction (X direction), the optical configuration can be easily downsized. Since the exit surface 11b of the first prism 11 is flat, the image light L1 is totally reflected by the exit surface 11b and then reflected by the powerful hologram surface 11c. That is, in the first prism 11, the image light L1 that has entered from the entrance surface 11a is reflected from the exit surface 11b first after being reflected twice by total reflection on the exit surface 11b and diffraction reflection on the hologram surface 11c. By exiting from the prism 11, the light enters the pupil of the observer eye EY.

  As the condition setting related to the conditional expression (8), the exit pupil EP (the pupil of the observer's eye EY) is arranged from the exit surface 11b of the prism 11 in the optical path of the principal ray emitted from the center of the screen 20a of the liquid crystal display element 20. The optical path length K (FIG. 3) up to.) Is preferably larger than 18 mm and smaller than 30 mm. The distance from the eye of the person wearing glasses to the eyeglass lens is generally 12 mm. Further, it is assumed that the lens thickness is 3 mm, and a margin of 3 mm is secured from the glasses to the prism 11. As described above, this corresponds to the lower limit of the conditional expression (8). In addition, the upper limit of conditional expression (8) is a value for preventing the glasses and the first prism 11 from being separated and easily displaced. In Example 1 described later, K is 23 mm.

  The first prism 11 guides the image light L1 incident from the liquid crystal display element 20 via the flat PBS 24 inside, and transmits the light of the external image (external light). The first prism 11 has a wedge shape that is thicker toward the upper end and thinner toward the lower end, and is joined to the second prism 12 with an adhesive 14 so as to sandwich the hologram optical element 13 therebetween. A parallel plate is formed. That is, the exit surface 11b of the first prism 11 and the prism surface 12a of the second prism 12 are parallel to each other. In this way, the second prism 12 is bonded to the first prism 11 so that both surfaces of the prism are parallel to each other, so that refraction when external light passes through the wedge-shaped portion of the first prism 11 is reduced to the second prism. 12 can be canceled, and distortion of the observed external field image can be prevented.

  In the image display device 1 shown in FIG. 1, the relationship between the focal length P of the hologram surface 11 c with power, the focal length S of the Fresnel lens 23, and the size L of the LED light source 21 in the folded section is a conditional expression. (3) is satisfied (FIG. 2). The size of a human pupil is generally 3 to 4 mm. By making the exit pupil EP larger than that, the viewer can easily see the pupil. In Example 1 described later, P / S × L = 8.8, which is a sufficiently large value.

  In the image display device 1 shown in FIG. 1, the relationship between the size H of the liquid crystal display element 20 in the folded section and the focal length P of the holographic surface 11c with power satisfies the conditional expression (4) ( Figure 2). Conditional expression (4) is a condition for showing a large screen to the observer, and H / P = 0.21 in Example 1 described later.

  In the image display device 1 shown in FIG. 1, in the principal ray of the light beam incident on the center of the screen 20a of the liquid crystal display element 20, the distance D1 from the exit surface of the Fresnel lens 23 to the flat PBS 24 and the liquid crystal display from the flat PBS 24 The relationship with the distance D2 to the element 20 satisfies the conditional expression (6) (FIG. 2). Conditional expression (6) is a condition setting for maintaining the center of gravity of the entire optical system in the vicinity of the prism. By satisfying conditional expression (6), a display such as an HMD equipped with an image display device is mounted. This can prevent misalignment. If the range of the conditional expression (6) is not satisfied, the mounting deviation is likely to occur. In Example 1 described later, D2 / D1 = 1.4.

  The image display device 1 shown in FIG. 1 satisfies the conditional expression (7) that defines the preferred size of the Fresnel lens 23 when the human pupil is 4 mm (FIG. 2). The lower limit of the conditional expression (7) is a condition setting relating to the size of the Fresnel lens 23 to ensure a sufficient pupil size, and the upper limit of the conditional expression (7) is that the diameter of the Fresnel lens 23 is increased. This is a condition setting for preventing the center of gravity from shifting too far to the eye side. In Example 1 described later, P × T / (D1 + D2) = 11.

  In the image display device 1 shown in FIG. 1, an angle M formed between the normal line of the hologram surface 11c and the lower marginal ray LM of the screen lower field angle (FIGS. 3 and 6) satisfies the conditional expression (9). . This is a condition setting for reducing the size of the first prism 11 by making the hologram surface 11c and the lower marginal ray LM of the lower screen angle of view substantially parallel to each other. The upper limit of conditional expression (9) (FIG. 6B, state α1) is that the hologram surface 11c (straight line on the paper surface) and the lower marginal ray LM on the lower screen angle of view do not intersect within the first prism 11. The lower limit (FIG. 6C, state α2) of conditional expression (9) is a condition setting for preventing the first prism 11 from becoming large. In Example 1 described later, M = 92 degrees.

  The image display device 1 shown in FIG. 1 satisfies the conditional expressions (10) and (11) that define the preferred sizes of the physical optical path lengths L1 and L2 (FIG. 3). These conditional expressions (10) and (11) are also condition settings for preventing an increase in the size of the prism, and in Example 1 described later, L1 = 1.1 mm and L2 = 3.2 mm.

  In the image display apparatus 1 shown in FIG. 1, the reflective surface 11c having the power of the first prism 11 in the optical path of the upper marginal ray of the upper field angle of the screen 20a of the liquid crystal display element 20 and the thickness B of the second prism 12. The ratio of the distance D to the exit surface 11b satisfies the conditional expressions (12) and (12a) (FIG. 3). These conditional expressions (12) and (12a) define a preferable range of conditions for achieving both a high visibility and a thin prism as described above.

  By adhering the second prism 12 to the first prism 11, both surfaces of the prism can be kept parallel (FIG. 3). However, if the lower limit of the conditional expression (12) is not reached and bonding is performed so that the entire extension line of the hologram surface 11c is covered with the second prism 12, the upper field of view can be secured, but the prism becomes thick and the weight increases. FIG. 7 shows a state in which the second prism 12 is maximized within a range satisfying the conditional expression (12). The lower limit of conditional expression (12) corresponds to the case where the thickness B of the second prism 12 is 10 mm. On the other hand, if the upper limit of the conditional expression (12) is exceeded and bonding is performed so as to cover only the light beam region using the second prism 12, it is difficult to ensure the upper field of view while reducing the weight. FIG. 8 shows a state where the second prism 12 is minimized within a range satisfying the conditional expression (12).

  Conditional expression (12) defines the condition range for achieving these balances, and conditional expression (12a) defines a more preferable condition range. The upper limit of conditional expression (12a) corresponds to the case where the thickness B of the second prism 12 is 7 mm, and the lower limit of conditional expression (12a) corresponds to the case where the thickness B of the second prism 12 is 8 mm. In Example 1 described later, D / B = 0.86.

  The hologram optical element 13 constitutes a combiner that simultaneously guides the display image IM displayed on the screen 20a of the liquid crystal display element 20 and the external image to the observer's eye EY. Thus, the display image IM and the external image provided from the liquid crystal display element 20 can be observed simultaneously. Therefore, by mounting the above-described image display device 1 (FIG. 1), an optical see-through display having a function of projecting and displaying the display image IM on the observer eye EY with the optical device 10 can be configured.

  As described above, it is desirable that the image display device 1 is mounted on the optical see-through display so that the hologram optical element 13 has a function of projecting and displaying the display image IM on the observer eye EY. In addition, the optical see-through display includes a support member that supports the image display device 1 so that the hologram optical element 13 is positioned in front of the observer's eye EY (that is, supports the image display device 1 in front of the observer's eyes). It is desirable that Since the image display device 1 has a high see-through property, a high video display effect can be obtained by arranging the image IM in front of the eyes of the observer. Examples of the optical see-through display include a head mounted display (HMD) and a head-up display (HUD). In addition, examples of the head-mounted display include spectacles and helmets, and examples of the use of the head-up display include driving an automobile and flying an airplane. Here, an eyeglass-type head-mounted display provided with the image display device 1 will be described as an example.

  FIG. 4 shows a schematic configuration of a glasses-type head mounted display 2 provided with the image display device 1. The head mounted display 2 includes the image display device 1 and the support member 3 described above. The liquid crystal display element 20 and the illumination device (LED light source 21, diffusing plate 22, Fresnel lens 23, etc.) of the image display device 1 are accommodated in the housing 7, and the upper end portion of the optical device 10 that is an eyepiece optical system. Is also located in the housing 7. The optical device 10 is configured by bonding the two prisms 11 and 12 as described above, and has a shape like one lens of a pair of glasses (lens for the right eye in FIG. 4) as a whole.

  In addition, the liquid crystal display element 20, the LED light source 21 and the like in the housing 7 are connected to a circuit board (not shown) via a cable 8 provided through the housing 7, and the liquid crystal is transmitted from the circuit board to the liquid crystal. Driving power and video signals are supplied to the display element 20, the LED light source 21, and the like. The image display device 1 further includes an imaging device that captures still images and moving images, a microphone, a speaker, an earphone, and the like, and information on the captured image and the display image via an external server or terminal and a communication line such as the Internet. Or a configuration for exchanging (transmitting / receiving) audio information.

  The support member 3 is a support mechanism corresponding to a frame of glasses, and supports the image display device 1 in front of the eyes of the observer (in front of the right eye in FIG. 4). The support member 3 includes temples 4R and 4L that are in contact with the left and right temporal regions of the observer, and nose pads 5R and 5L that are in contact with the nose of the observer. The support member 3 also supports the lens 6 in front of the left eye of the observer, but this lens 6 is a dummy lens.

  When the head mounted display 2 is mounted on the observer's head and the image IM is displayed on the liquid crystal display element 20, the image light L1 is guided to the exit pupil EP (FIG. 1) via the optical device 10. Accordingly, by aligning the observer's pupil (observer eye EY) with the position of the exit pupil EP, the observer can observe an enlarged virtual image of the display image IM of the image display device 1. At the same time, the observer can observe an external image through the optical device 10 with see-through. In addition, you may enable it to observe an image | video with both eyes using two image display apparatuses 1. FIG.

  As described above, when the image display device 1 is supported by the support member 3, the observer observes the display image IM and the external image provided from the image display device 1 simultaneously and stably for a long time without hands. It is possible to perform a desired operation with open hands.

  Hereinafter, the configuration and the like of the image display apparatus embodying the present invention will be described more specifically with reference to the construction data of the examples. Examples 1 and 2 (EX1 and 2) listed here are numerical examples corresponding to the above-described embodiments of the image display device, and their schematic cross-sectional views (FIG. 1 and the like) are optical images of Examples 1 and 2. The arrangement, optical path, etc. are shown. In addition, FIG. 9 shows Embodiments 1 and 2 of the image display device with optical surfaces and optical paths, and FIGS. 10 and 11 show optical arrangements, optical paths, etc. of Embodiments 3 and 4 (EX3 and 4) of the image display device. As in FIG. 1, it is shown in schematic cross section.

  Tables 1, 4 and 7 show the construction data of each example. In the construction data, in order from the left column, surface number i (i = 0, 1, 2,..., 22; OBJ: object surface, STO: aperture, IMG: image surface), radius of curvature in mm (mm) ), Radius of curvature (mm) in the X direction, optical action (reflection, refraction), refractive index and Abbe number with respect to a wavelength of 532 nm. The surface Si (surface number i = 0, 1, 2,..., 22) is the i-th surface counted from the object surface OBJ side in the optical path from the object surface OBJ (S0) to the image surface IMG (S22). Therefore, the stop STO corresponds to the exit pupil EP, and the image plane IMG corresponds to the liquid crystal screen (image display plane) 20a for displaying the image IM. The curvature radii in the Y direction and the X direction are the coordinate axis directions in the orthogonal coordinate system (X, Y, Z) in which the surface vertex of each optical surface Si is the origin and the normal line at the surface vertex is the Z axis. is there. The relationship between the optical surface Si and the optical element (FIGS. 10 and 11) in Examples 3 and 4 is the same as the relationship between the optical surface Si (FIG. 9) and the optical element (FIG. 1) in Examples 1 and 2. It is.

  Tables 2, 5 and 8 show the arrangement data of the surface Si in each example. The arrangement of each surface Si is specified by the surface vertex coordinates (X, Y, Z) in the eccentricity data based on the first surface S1 and the rotation angle around the X axis. The surface vertex coordinates of the optical surface Si are the local orthogonality in the orthogonal coordinate system (X, Y, Z) of the global first surface S1, with the surface vertex being the origin of the local orthogonal coordinate system (X, Y, Z). It is represented by the coordinates of the origin of the coordinate system (X, Y, Z) (unit: mm), and the inclination of each optical surface Si is represented by the rotation angle around the X axis centered on the surface vertex ( (Unit: °) The counterclockwise direction with respect to the positive direction of the X, Y, and Z axes is the positive direction of the rotation angle of the X, Y, and Z rotations.

  However, the coordinate systems are all defined by the right-hand system, and the global orthogonal coordinate system (X, Y, Z) of the first surface S1 is not limited to the first surface S1 but the fourth surface S4 (aperture STO). This is an absolute coordinate system that is consistent with the orthogonal coordinate system (X, Y, Z). Further, the reference direction of the rotation angle around the coordinate axis (that is, the coordinate axis direction before the rotation) is the coordinate axis direction in the orthogonal coordinate system (X, Y, Z) of the first surface S1. Therefore, in the first surface S1 and the fourth surface S4 in FIG. 9, the X direction is the direction perpendicular to the paper surface (the left-right direction of the angle of view), and the Y direction is the vertical direction of the paper surface (the vertical direction of the angle of view). The back direction is the + X direction, the upward direction on the paper is the + Y direction, and the right direction on the paper is the + Z direction.

Tables 3, 6 and 9 show the phase difference coefficient Cj of the sixth surface S6 in each example. The sixth surface S6 is the hologram surface 11c, and the phase difference function of the hologram is represented by a polynomial f (x, y) represented by the following equation (DS). However, in the local orthogonal coordinate system (x, y, z) having the origin (plane vertex) on the optical axis (z axis) of the sixth surface S6 as the origin, the back direction of the paper surface is the + x direction, and the optical axis is within the paper surface. Is a + y direction (right-handed system), and m + n ≦ 10, j = {(m + n) ² + m + 3n} / 2. Note that the normalized wavelength of the phase difference function f (x, y) is 532 nm, and E−n = × 10 ⁻ⁿ for all data.

  Table 10 shows correspondence data of each conditional expression and related data for each example. As can be seen from the data in Table 10, the basic configuration of the second embodiment is the same as that of the first embodiment. The difference from the first embodiment is that the corresponding value of conditional expression (5), that is, the focal length S of the Fresnel lens 23 (illumination optical system) is 8.0 mm. With the focal length S of this size, it is possible to avoid the LED light source 21 from interfering with the forehead or glasses of the observer. Even in that case, the LED light source 21 is arranged at the focal position of the Fresnel lens 23. When the focal length S of the Fresnel lens 23 is 8.0 mm, the corresponding value of the conditional expression (3) is P / S × L = 7.9> 4. Since the conditional expression (3) is satisfied, a sufficient pupil EP size is secured.

  In Example 3, Conditional Expression (2) is satisfied near its upper limit, and in Example 4, Conditional Expression (2) is satisfied near its lower limit. If the upper limit of conditional expression (2) is exceeded (φ ≧ 47 degrees), the Fresnel lens 23 (illumination optical system) and the planar PBS 24 are likely to interfere with each other. If the lower limit of conditional expression (2) is not reached (φ ≦ 30 degrees), the Fresnel lens 23 (illumination optical system) and the reflective liquid crystal display element 20 are likely to interfere with each other, and the optical system may not be established.

1 Image display device 2 Head mounted display (optical see-through display)
3 Support Member 10 Optical Device 11 First Prism 11a Incident Surface 11b Ejection Surface 11c Hologram Surface (Power Reflecting Surface)
12 Second prism 13 Hologram optical element 14 Adhesive 20 Liquid crystal display element 20a Screen 21 LED light source 22 Diffuser (illumination optical system)
23 Fresnel lens (illumination optical system)
24 Planar PBS (Polarized Beam Splitter)
ES light source EG liquid crystal screen E1 illumination optical system E2 powerful reflective surface L0 illumination light L1 image light IM display image EY observer eye EP exit pupil

Claims (17)

A light source that emits illumination light, an illumination optical system that collimates incident light, a planar polarization beam splitter that performs polarization separation of incident light, and a reflective liquid crystal display that performs spatial modulation on the incident light for image display An element, and a prism that causes incident light incident from the incident surface to exit from the exit surface after being reflected twice.
The prism has a reflective surface with power,
Illumination light from the light source is collimated by the illumination optical system, the collimated illumination light is reflected by the polarization beam splitter, and the reflected illumination light is spatially modulated by the liquid crystal display element to generate image light. The image light is incident on the prism from the incident surface after being transmitted by the polarization beam splitter, and the image light is reflected by the reflecting surface having the power after being reflected by the emitting surface. An image display device that emits out of the prism and enters the pupil of an observer,
When a plane including the chief ray of illumination light just before incidence on the center of the screen of the liquid crystal display element and the chief ray of image light just after reflection is a folded section,
The following conditional expression (1) is satisfied for all principal rays in the folded section:
An image display device satisfying the following conditional expressions (2) to (7):
0 <θ <5 (1)
30 <φ <47 (2)
P / S × L> 4 (3)
H / P> 0.2 (4)
S <9 (5)
0.43 <D2 / D1 <2.2 (6)
4.0 <P × T / (D1 + D2) <25 (7)
However,
θ: the incident angle (degrees) of the principal ray with respect to the screen of the liquid crystal display element in the folded section,
φ: Angle (degrees) between the normal of the polarization separation plane of the polarizing beam splitter and the normal of the screen of the liquid crystal display element,
P: focal length (mm) of the reflecting surface with power,
S: Focal length of illumination optical system (mm),
L: the size (mm) of the light source in the folded section,
H: size of liquid crystal display element in folded section (mm),
D1: distance (mm) from the exit surface of the illumination optical system to the polarization beam splitter in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
D2: distance (mm) from the polarizing beam splitter to the liquid crystal display element in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
T: the size (mm) of the illumination optical system that occupies the folded section in the direction perpendicular to the optical axis of the illumination optical system,
It is. The image display device according to claim 1, wherein the following conditional expression (7a) is satisfied:
4.0 <P × T / (D1 + D2) <13 (7a)
However,
P: focal length (mm) of the reflecting surface with power,
T: the size (mm) of the illumination optical system that occupies the folded section in the direction perpendicular to the optical axis of the illumination optical system,
D1: distance (mm) from the exit surface of the illumination optical system to the polarization beam splitter in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
D2: distance (mm) from the polarizing beam splitter to the liquid crystal display element in the principal ray of illumination light incident on the center of the screen of the liquid crystal display element;
It is.   3. The image display device according to claim 1, wherein the power reflecting surface provided on the prism is only one surface, and the polarizing beam splitter is joined to the incident surface of the prism. . The image display device according to claim 1, wherein the following conditional expression (8) is satisfied:
18 <K <30 (8)
However,
K: optical path length (mm) from the exit surface of the prism to the exit pupil in the optical path of the principal ray exiting from the center of the screen of the liquid crystal display element;
It is.   The image display apparatus according to claim 1, wherein the reflective surface having power is a hologram surface.   6. The image display device according to claim 5, wherein the hologram surface has a shape having a curvature only in a direction perpendicular to an eccentric direction. The image display device according to claim 5, wherein the following conditional expression (9) is satisfied:
83 <M <120 (9)
However,
M: Angle (degrees) between the normal of the hologram surface and the lower marginal ray of the screen angle of view of the liquid crystal display element,
It is. The image display device according to claim 1, wherein the following conditional expression (10) is satisfied:
L1 <2.0 (10)
However,
L1: Physical optical path length (mm) from the reflection position on the exit surface of the prism to the reflective surface with power in the optical path of the lower marginal ray of the lower screen angle of view of the liquid crystal display element;
It is. The image display device according to claim 1, wherein the following conditional expression (11) is satisfied:
L2 <5.0 (11)
However,
L2: physical optical path length (mm) from the incident surface of the prism to the reflection position on the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is.   The image display device according to claim 1, wherein an LED light source is disposed as the light source in the vicinity of a focal position of the illumination optical system.   The image display apparatus according to claim 1, wherein the illumination optical system includes a Fresnel lens that is a single lens.   The illumination optical system has a diffuser plate that is diffusible in a direction perpendicular to the folded section, and an independent LED light source corresponding to the three primary colors RGB is arranged in the direction perpendicular to the folded section as the light source. The image display device according to claim 1, wherein the image display device is an image display device.   The image according to any one of claims 1 to 12, further comprising a second prism adhered to the reflective surface having power so as to have a prism surface parallel to the exit surface. Display device. The image display device according to claim 1, wherein the following conditional expression (12) is satisfied:
0.65 <D / B <1.0 (12)
However,
B: thickness of second prism (mm),
D: distance (mm) from the reflecting surface having the power of the prism to the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is. The image display device according to claim 1, wherein the following conditional expression (12a) is satisfied:
0.8 <D / B <0.9 (12a)
However,
B: thickness of second prism (mm),
D: distance (mm) from the reflecting surface having the power of the prism to the exit surface in the optical path of the upper marginal ray of the on-screen angle of view of the liquid crystal display element;
It is.   By mounting the image display device according to any one of claims 1 to 15, a function of projecting and displaying a display image of the liquid crystal display element on the observer's eye on the hologram surface is provided. Optical see-through display.   The optical see-through display according to claim 16, further comprising a support member that supports the image display device so that the hologram surface is positioned in front of an observer's eye.

Images