Optical system and display unit

Abstract

To provide an optical system and a display unit that can reduce deterioration of a display element due to strong light incident from an eyepiece part opening when not in use, without being increased in size in an optical axis direction.SOLUTION: An optical system has a polarization-selective semi-transparent reflection element, a first 1 / 4 wavelength plate, an optical member including the semi-transparent reflection element, a second 1 / 4 wavelength plate, and a polarizer, which are arranged in order from a side of an exit pupil to a side of a display element, and the optical system guides light from the display element to the exit pupil. The optical system can be changed to a first state where the polarization directions of the polarization-selective semi-transparent reflection element and the polarizer are orthogonal to each other, and a second state where the polarization directions of the polarization-selective semi-transparent reflection element and the polarizer match each other.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an optical system of a display device that is placed mainly on the head or face of a viewer and displays an image in front of the viewer's eyes. [Background technology]

[0002] In a head mounted display (HMD), strong light such as sunlight may enter through the eyepiece opening when not in use, and may be concentrated on the surface of the display element, causing the display element to burn and deteriorate. This phenomenon is also a problem in electronic viewfinders and image sensors, and measures have been taken to prevent this from happening. Patent Document 1 discloses a configuration in which the eyepiece is moved in the direction of the optical axis so that incident sunlight is not concentrated on the display element when not in use. Patent Document 2 discloses a configuration in which two polarizing filters are placed between the lens mount and the image sensor, and one filter is rotated in conjunction with the attachment / detachment / rotation of an interchangeable lens, thereby attenuating the light entering the image sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-153048 A [Patent Document 2] JP 2019-23683 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the configuration of Patent Document 1, the lens needs to be moved in the optical axis direction, which increases the size of the main body in the optical axis direction. Also, in the configuration of Patent Document 2, the device is increased in size in the optical axis direction by arranging two polarizing filters, and there is a risk that the polarizing filters, which are not actually necessary for shooting, may affect the image quality of the captured image.

[0005] An object of the present invention is to provide an optical system and a display device that can reduce degradation of a display element caused by strong light entering through an eyepiece opening when not in use, without increasing the size in the optical axis direction. [Means for solving the problem]

[0006] An optical system as one aspect of the present invention has a polarization-selective semi-transmissive reflector, a first quarter-wave plate, an optical member including a semi-transmissive reflector, a second quarter-wave plate, and a polarizer arranged in that order from the exit pupil side to the display element side, and guides light from the display element to the exit pupil, characterized in that the optical system is changeable between a first state in which the polarization directions of the polarization-selective semi-transmissive reflector and the polarizer are perpendicular to each other, and a second state in which the polarization directions of the polarization-selective semi-transmissive reflector and the polarizer are the same. Effect of the Invention

[0007] According to the present invention, it is possible to provide an optical system and a display device that can reduce deterioration of a display element caused by strong light entering through an eyepiece opening when not in use, without increasing the size in the optical axis direction. [Brief description of the drawings]

[0008] [Figure 1] 1 is a front perspective view of an image display device according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a rear perspective view of the image display device according to the embodiment of the present invention. [Diagram 3] FIG. 2 is a cross-sectional view of a lens of an eyepiece optical system. [Figure 4] FIG. 2 is an explanatory diagram of an optical path of an observation optical system that uses polarized light. [Diagram 5] 4 is an explanatory diagram of the optical path of the observation optical system when the image display device is in use and external light is incident on the display panel. FIG. [Figure 6] 4 is an explanatory diagram of the optical path of the observation optical system when the image display device is in use and external light is incident on the display panel. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to refer to the same components, and duplicated descriptions will be omitted.

[0010] 1 and 2 are respectively a front perspective view and a rear perspective view of a head mounted display (hereinafter, HMD) 100, which is an example of an image display device according to an embodiment of the present invention. The Z-axis direction is a direction parallel to each optical axis of a pair of eyepiece optical systems (optical systems). The X-axis direction is a direction connecting the two optical axis centers of the pair of eyepiece optical systems. The Y-axis direction is a direction perpendicular to the X-axis direction and the Z-axis direction.

[0011] The HMD100 is a video see-through head-mounted display that seamlessly fuses real space and virtual space in real time to provide mixed reality and augmented reality. The HMD100 captures an external image (optical image) observed by an observer through an imaging optical system with an imaging element, and displays a display image in which a computer graphic (CG) image is superimposed on the captured image on a display element. The observer can observe the display image through an eyepiece optical system. If the optical axis of the eyepiece optical system and the optical axis of the imaging optical system in the HMD100 are misaligned, the observer feels uncomfortable with the displayed image. If the HMD100 becomes larger in the optical axis direction, the observer is more likely to feel uncomfortable with the displayed image or feel uncomfortable when wearing it. In order to suppress the misalignment between the optical axis of the eyepiece optical system and the optical axis of the imaging optical system, it is important to make the HMD100 thin. Furthermore, by making the HMD100 thin, the usability when wearing it can be improved. The HMD 100 can be worn on the observer's head or face by a band-shaped or eyeglass-shaped attachment part.

[0012] The HMD100 has a pair of eyepiece optical systems 10L and 10R corresponding to the left and right eyes of the observer. The eyepiece optical systems 10L and 10R are covered by an exterior member 20. Images with parallax for the left and right eyes are projected onto the eyepiece optical systems 10L and 10R, respectively, and the observer can view a stereoscopic image. An operation member 30 operated by the observer is mounted on the top surface of the HMD100. The operation member 30 is used to turn the device power on and off, select items, change parameters, and the like. Two types of camera units, each with a different purpose, are mounted on the front surface of the HMD100. The objective camera units 40L and 40R, which serve as imaging optical systems, correspond to the eyepiece optical systems 10L and 10R, respectively, and acquire images for the left and right eyes. It is desirable that the objective camera units 40L and 40R are cameras capable of capturing high-resolution color images. The position detection camera units 41L and 41R detect the position and orientation of the HMD100 in real space. When using CG images superimposed on images captured by the objective camera units 40L and 40R, it is necessary to quickly switch the projected images in response to the observer's body movements. Therefore, it is desirable for the position detection camera unit 41 to be a camera capable of capturing images with little distortion at a high frame rate.

[0013] 2, the HMD 100 may have eyecups 50L, 50R that cover the side portions of the eyepiece optical systems 10L, 10R. The eyecups 50L, 50R reduce the disruption of image viewing caused by light incident from the side of the observer's face being reflected on the surfaces of the eyepiece optical systems 10L, 10R. The HMD 100 is connected to an external communication device such as a PC or a battery via a communication cable 60, and is supplied with power and data related to the image to be projected on the display panel (display element) of the eyepiece optical systems 10L, 10R.

[0014] The lens configuration of the eyepiece optical systems 10L and 10R and the optical path using polarized light when the HMD 100 is in use will be described below.

[0015] 3 is a lens cross-sectional view of the eyepiece optical systems 10L and 10R. Each of the eyepiece optical systems 10L and 10R includes a first lens 102, a second lens (optical member) 103, a second quarter-wave plate 104, a polarizer 105, and a display panel 106, which are arranged in this order from the exit pupil 101 side to the display panel 106 side. On the surface of the first lens 102 on the exit pupil 101 side, a polarization selective semi-transmissive reflector (hereinafter, referred to as a Polarizing Beam Splitter (PBS)) 102a and a first quarter-wave plate 102b are arranged in this order from the exit pupil 101 side to the display panel 106 side. The surface of the first lens 102 on the exit pupil side functions as a first semi-transmissive reflector. Also, on the surface of the second lens 103 on the exit pupil 101 side, a half mirror 103a is arranged as a semi-transmissive reflector. The surface of the second lens 103 on the side of the exit pupil 101 functions as a second semi-transmissive reflective surface.

[0016] The PBS 102a is, for example, a wire grid polarizer configured to reflect linearly polarized light polarized in the same direction as when the light passes through the polarizer 105 and transmit linearly polarized light polarized in a direction perpendicular to the direction. The wire grid forming surface of the PBS 102a functions as a semi-transmissive reflective surface. The first quarter-wave plate 102b and the second quarter-wave plate 104 are arranged with their slow axes tilted at 90 degrees, and the second quarter-wave plate 102b is arranged with its slow axis tilted at 45 degrees with respect to the polarization transmission axis of the polarizer 105. The half mirror 103a is, for example, a half mirror formed of a dielectric multilayer film and functions as a semi-transmissive reflective surface.

[0017] The eyepiece optical systems 10L and 10R can be changed between a first state (a state in use) in which the polarization directions of the PBS 102a and the polarizer 105 are orthogonal to each other, and a second state (a state not in use) in which the polarization directions of the PBS 102a and the polarizer 105 are the same. In this embodiment, the eyepiece optical systems 10L and 10R can be changed between the first state and the second state by changing the phase of the polarizer 105 (changing the polarization direction of the polarizer 105). Note that "orthogonal" includes not only strictly orthogonal but also practically orthogonal (approximately orthogonal). Furthermore, "matching" includes not only strictly matching but also practically matching (approximately matching).

[0018] In this embodiment, the eyepiece optical systems 10L and 10R are changed between a first state and a second state according to the state of the HMD 100. The state of the HMD 100 is, for example, a power ON / OFF state or a sleep mode. For example, the eyepiece optical systems 10L and 10R are changed to the first state when the power is ON, and the eyepiece optical systems 10L and 10R are changed to the second state when the power is OFF. In addition, when each eyepiece optical system is in the first state and the attitude of the HMD 100 is maintained for a predetermined time or more in a state in which the direction from the display panel 106 side to the exit pupil 101 side is vertically upward. Note that the direction from the display panel 106 side to the exit pupil 101 side does not have to be vertically upward strictly, and it is sufficient if it is substantially vertically upward.

[0019] 4 is an explanatory diagram of the optical path of an observation optical system using polarized light. The light emitted from the display panel 106 is unpolarized light, and only linearly polarized light polarized in a first direction (first polarization direction) by the polarizer 105 passes through the polarizer 105. The light that passes through the polarizer 105 is converted into circularly polarized light by the second quarter-wave plate 104, and is split by the half mirror 103a into reflected light (first reflected light on optical path A) and transmitted light (first transmitted light on optical path B).

[0020] The first reflected light on optical path A is reflected by half mirror 103a to become reverse-circularly polarized light, and returns to second quarter-wave plate 104. The reverse-circularly polarized light that has returned to second quarter-wave plate 104 passes through second quarter-wave plate 104 and becomes linearly polarized light polarized in a second direction (second polarization direction) perpendicular to the first direction, and is absorbed by polarizer 105.

[0021] The first transmitted light in the optical path B is transformed into linearly polarized light polarized in a first direction by the first quarter-wave plate 102b after passing through the half mirror 103a, and enters the PBS 102a. The linearly polarized light polarized in the first direction is reflected by the PBS 102a due to the polarization selectivity of the PBS 102a. The light reflected by the PBS 102a is transformed into circularly polarized light by the first quarter-wave plate 102b, and enters the half mirror 103a. The light reflected by the half mirror 103a is transformed into circularly polarized light in the opposite direction to the light before reflection, and enters the first quarter-wave plate 102b to become linearly polarized light polarized in a second direction, and enters the PBS 102a. The linearly polarized light polarized in the second direction is transmitted through the PBS 102a and guided to the exit pupil 101 due to the polarization selectivity of the PBS 102a.

[0022] With the above configuration, only light that is transmitted through the second semi-transmissive reflective surface, reflected by the first semi-transmissive reflective surface, reflected by the second semi-transmissive reflective surface, and transmitted through the first semi-transmissive reflective surface is guided to the exit pupil 101.

[0023] The optical path along which external light incident on the eyepiece optical systems 10L and 10R from the exit pupil 101 is focused on the display panel 106 when the HMD 100 is in use will be described below.

[0024] 5 is an explanatory diagram of the optical path of the observation optical system when external light is incident on the display panel 106 while the HMD 100 is in use. The external light incident from the exit pupil 101 is unpolarized light, and only linearly polarized light polarized in a second direction by the PBS 102a passes through the PBS 102a. The light that passes through the PBS 102a becomes circularly polarized light by the first quarter-wave plate 102b, and is split by the half mirror 103a into transmitted light (second transmitted light on optical path C) and reflected light (second reflected light on optical path D).

[0025] The second transmitted light on the optical path C passes through the half mirror 103 a, and is then polarized in the second direction by the second quarter-wave plate 104 to become linearly polarized light, and is absorbed by the polarizer 105 .

[0026] The second reflected light on the optical path D becomes circularly polarized light in the opposite direction to the light before reflection, enters the first quarter-wave plate 102b, becomes linearly polarized light polarized in the first direction, and enters the PBS 102a. The linearly polarized light polarized in the first direction is reflected by the PBS 102a due to the polarization selectivity of the PBS 102a. The light reflected by the PBS 102a becomes circularly polarized light by the first quarter-wave plate 102b, and enters the half mirror 103a. The light transmitted through the half mirror 103a becomes linearly polarized light polarized in the first direction by the second quarter-wave plate 104, transmits through the polarizer 105, and enters the display panel 106.

[0027] With the above configuration, only light that is transmitted through the first semi-transmissive reflective surface, reflected by the second semi-transmissive reflective surface, reflected by the first semi-transmissive reflective surface, and transmitted through the second semi-transmissive reflective surface is guided to the display panel 106. Note that the light that is incident on the display panel 106 along the above optical path is focused on the surface of the display panel 106 by the first lens 102 and the second lens 103. Therefore, if the natural light that is incident on the exit pupil 101 is high-intensity light such as sunlight, the surface of the display panel 106 may deteriorate.

[0028] Hereinafter, a method for reducing deterioration of the display panel 106 by changing the polarization direction of the polarizer 105 when the HMD 100 of this embodiment is not in use will be described. When changing the polarization direction of the polarizer 105, the element itself may be rotated by 90 degrees. Also, when the polarizer 105 is an element that utilizes the polarization characteristics of liquid crystal, the polarization direction may be changed by changing the state of application of voltage to the polarizer 105.

[0029] 6 is an explanatory diagram of the optical path of the observation optical system when the HMD 100 is not in use and external light is incident on the display panel 106. In this embodiment, when the HMD 100 is not in use, the polarizer 105 is rotated 90 degrees from the state when the HMD 100 is in use (the state in FIG. 5).

[0030] The external light incident from the exit pupil 101 is unpolarized light, and only the linearly polarized light polarized in the second direction by the PBS 102a is transmitted through the PBS 102a. The light transmitted through the PBS 102a is circularly polarized by the first quarter-wave plate 102b, and is split by the half mirror 103a into transmitted light (the second transmitted light on the optical path C) and reflected light (the second reflected light on the optical path D).

[0031] The second transmitted light on optical path C passes through half mirror 103a, and then becomes linearly polarized light polarized in the second direction by second quarter-wave plate 104. At this time, since polarizer 105 is rotated 90 degrees with respect to the state in FIG. 5, the linearly polarized light polarized in the second direction passes through polarizer 105 and enters display panel 106.

[0032] The second reflected light on the optical path D becomes circularly polarized light in the opposite direction to the light before reflection, enters the first quarter-wave plate 102b, becomes linearly polarized light polarized in the first direction, and enters the PBS 102a. The linearly polarized light polarized in the first direction is reflected by the PBS 102a due to the polarization selectivity of the PBS 102a. The light reflected by the PBS 102a becomes circularly polarized light by the first quarter-wave plate 102b, and enters the half mirror 103a. The light transmitted through the half mirror 103a becomes linearly polarized light polarized in the first direction by the second quarter-wave plate 104, and enters the polarizer 105. At this time, the polarizer 105 is rotated 90 degrees from the state of FIG. 5, so the linearly polarized light polarized in the first direction is absorbed by the polarizer 105.

[0033] With the above configuration, only the light transmitted through the first semi-transmissive reflective surface and the second semi-transmissive reflective surface is guided to the display panel 106. Note that the light incident on the display panel 106 along the above optical path is not condensed on the surface of the display panel 106 by the first lens 102 and the second lens 103. Therefore, even if the natural light incident on the exit pupil 101 is high-intensity light such as sunlight, deterioration of the surface of the display panel 106 can be reduced.

[0034] The disclosure of this embodiment includes the following configuration.

[0035] (Configuration 1) An optical system including a polarization-selective semi-transmissive reflective element, a first quarter-wave plate, an optical member including a semi-transmissive reflective element, a second quarter-wave plate, and a polarizer, which are arranged in this order from an exit pupil side to a display element side, and which guides light from the display element to the exit pupil, The optical system is characterized in that it is changeable between a first state in which the polarization directions of the polarization-selective semi-transmissive reflector and the polarizer are perpendicular to each other, and a second state in which the polarization directions of the polarization-selective semi-transmissive reflector and the polarizer are the same. (Configuration 2) the polarization-selective semi-transmissive element reflects light having a first polarization direction and transmits light having a second polarization direction orthogonal to the first polarization direction; The optical system described in configuration 1, characterized in that in the first state, the polarizer transmits light of the first polarization direction and absorbs light of the second polarization direction, and in the second state, the polarizer absorbs light of the first polarization direction and transmits light of the second polarization direction. (Configuration 3) 3. The optical system according to claim 1, wherein in the second state, the polarizer absorbs light that is transmitted through the semi-transmissive reflective surface after being reflected by the polarization-selective semi-transmissive reflective element, out of external light that is transmitted through the semi-transmissive reflective surface. (Configuration 4) the first quarter-wave plate and the second quarter-wave plate are arranged with their slow axes inclined at 90 degrees; The optical system according to any one of configurations 1 to 3, wherein the second quarter-wave plate is arranged with its slow axis inclined at 45 degrees with respect to the polarization transmission axis of the polarizer. (Configuration 5) 5. The optical system according to any one of configurations 1 to 4, wherein the optical system can be changed between the first state and the second state by rotating the polarizer by 90 degrees. (Configuration 6) The polarizer is an element that utilizes the polarization properties of a liquid crystal, An optical system described in any one of configurations 1 to 4, characterized in that the optical system can be changed between the first state and the second state by changing the state of voltage applied to the polarizer. (Configuration 7) In the first state, the light from the display element is transmitted through the polarizer, transmitted through the second quarter-wave plate, and then split into a first reflected light that is reflected by the semi-transmissive reflective surface and a first transmitted light that is transmitted through the semi-transmissive reflective surface; the first reflected light is transmitted through the second quarter-wave plate and absorbed by the polarizer; the first transmitted light is transmitted through a first quarter-wave plate, reflected by the polarization-selective semi-transmissive reflector, transmitted through the first quarter-wave plate, reflected by the semi-transmissive reflecting surface, transmitted through the first quarter-wave plate, transmitted through the polarization-selective semi-transmissive reflector, and incident on the exit pupil; In the second state, external light is transmitted through the polarization selective semi-transmissive reflector and the first quarter-wave plate, and then split into a second transmitted light that is transmitted through the semi-transmissive reflecting surface and a second reflected light that is reflected by the semi-transmissive reflecting surface; the second transmitted light is transmitted through the second quarter-wave plate, transmitted through the polarizer, and incident on the display element; The optical system according to any one of configurations 1 to 6, wherein the second reflected light passes through the first quarter-wave plate, is reflected by the polarization-selective semi-transmissive reflecting element, passes through the first quarter-wave plate, passes through the semi-transmissive reflecting surface, passes through the second quarter-wave plate, and is absorbed by the polarizer. (Configuration 8) A display element; an optical system including a polarization selective semi-transmissive reflective element, a first quarter-wave plate, an optical member including a semi-transmissive reflective element, a second quarter-wave plate, and a polarizer, which are arranged in this order from an exit pupil side to a display element side, and which guides light from the display element to the exit pupil; The display device is characterized in that the optical system is changeable between a first state in which the polarization directions of the polarization-selective semi-transmissive reflector and the polarizer are perpendicular to each other, and a second state in which the polarization directions of the polarization-selective semi-transmissive reflector and the polarizer are the same. (Configuration 9) the polarization-selective semi-transmissive element reflects light having a first polarization direction and transmits light having a second polarization direction orthogonal to the first polarization direction; The display device described in configuration 9, characterized in that in the first state, the polarizer transmits light of the first polarization direction and absorbs light of the second polarization direction, and in the second state, the polarizer absorbs light of the first polarization direction and transmits light of the second polarization direction. (Configuration 10) The display device described in configuration 8 or 9, characterized in that in the second state, the polarizer absorbs light that is transmitted through the semi-transmissive reflective surface after being reflected by the polarization-selective semi-transmissive reflective element, of external light that is transmitted through the semi-transmissive reflective surface. (Configuration 11) the first quarter-wave plate and the second quarter-wave plate are arranged with their slow axes inclined at 90 degrees; 11. The display device according to any one of configurations 8 to 10, wherein the second quarter-wave plate is arranged with its slow axis inclined at 45 degrees with respect to the polarization transmission axis of the polarizer. (Configuration 12) A display device described in any one of configurations 8 to 11, characterized in that the optical system can be changed between the first state and the second state by rotating the polarizer by 90 degrees. (Configuration 13) The polarizer is an element that utilizes the polarization properties of a liquid crystal, 12. The optical system described in any one of configurations 8 to 11, characterized in that the optical system can be changed between the first state and the second state by changing the state of voltage applied to the polarizer. (Configuration 14) In the first state, the light from the display element is transmitted through the polarizer, transmitted through the second quarter-wave plate, and then split into a first reflected light that is reflected by the semi-transmissive reflective surface and a first transmitted light that is transmitted through the semi-transmissive reflective surface; the first reflected light is transmitted through the second quarter-wave plate and absorbed by the polarizer; the first transmitted light is transmitted through a first quarter-wave plate, reflected by the polarization-selective semi-transmissive reflector, transmitted through the first quarter-wave plate, reflected by the semi-transmissive reflecting surface, transmitted through the first quarter-wave plate, transmitted through the polarization-selective semi-transmissive reflector, and incident on the exit pupil; In the second state, external light is transmitted through the polarization selective semi-transmissive reflector and the first quarter-wave plate, and then split into a second transmitted light that is transmitted through the semi-transmissive reflecting surface and a second reflected light that is reflected by the semi-transmissive reflecting surface; the second transmitted light is transmitted through the second quarter-wave plate, transmitted through the polarizer, and incident on the display element; 14. The display device according to any one of configurations 8 to 13, wherein the second reflected light passes through the first quarter-wave plate, is reflected by the polarization-selective semi-transmissive reflective element, passes through the first quarter-wave plate, passes through the semi-transmissive reflective surface, passes through the second quarter-wave plate, and is absorbed by the polarizer. (Configuration 15) 15. The display device according to any one of configurations 8 to 14, wherein the optical system changes between the first state and the second state depending on the state of the image display device. (Configuration 16) A display device described in any one of configurations 8 to 15, characterized in that the optical system is in the first state when the power of the image display device is ON, and in the second state when the power of the image display device is OFF. (Configuration 17) A display device described in any one of configurations 8 to 16, characterized in that when the optical system is in the first state and the attitude of the image display device is maintained for a predetermined period of time or more in a state in which the direction from the display element side to the exit pupil side is vertically upward, the optical system changes to the second state. (Configuration 18) 18. The display device according to any one of configurations 8 to 17, characterized in that it can be worn on a viewer's head.

[0036] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0037] 10L,10R eyepiece optical system 101 Exit pupil 102a Polarization selective semi-transmissive reflector 102b First quarter wave plate 103 Second lens (optical component) 103a Half mirror (semi-transmissive reflective element) 104 Second quarter wave plate 105 Polarizer 106 Display panel (display element)

Claims

1. An optical system having a polarization-selective semi-transmissive reflective element, a first quarter-wave plate, an optical member including a semi-transmissive reflective surface, a second quarter-wave plate, and a polarizer, arranged in order from the side of the exit pupil to the side of the display element, for guiding light from the display element to the exit pupil, wherein the optical system is capable of changing between a first state in which the polarization directions of the polarization-selective semi-transmissive reflective element and the polarizer are orthogonal to each other and a second state in which the polarization directions of the polarization-selective semi-transmissive reflective element and the polarizer are the same.

2. The polarization-selective semi-transmissive reflective element reflects light having a first polarization direction and transmits light having a second polarization direction orthogonal to the first polarization direction, and the polarizer transmits light having the first polarization direction and absorbs light having the second polarization direction in the first state, and absorbs light having the first polarization direction and transmits light having the second polarization direction in the second state. The optical system according to claim 1, characterized in that.

3. In the second state, the polarizer absorbs light that is reflected by the polarization-selective semi-transmissive reflective element and then transmitted through the semi-transmissive reflective surface among the light transmitted through the semi-transmissive reflective surface of external light. The optical system according to claim 1 or 2, characterized in that.

4. The first quarter-wave plate and the second quarter-wave plate are arranged such that their slow axes are inclined by 90 degrees with respect to each other, and the second quarter-wave plate is arranged such that its slow axis is inclined by 45 degrees with respect to the polarization transmission axis of the polarizer. The optical system according to claim 1 or 2, characterized in that.

5. By rotating the polarizer by 90 degrees, the optical system is capable of changing between the first state and the second state. The optical system according to claim 1 or 2, characterized in that.

6. The polarizer is an element that utilizes the polarization characteristics of liquid crystal, and by changing the voltage application state to the polarizer, the optical system is capable of changing between the first state and the second state. The optical system according to claim 1 or 2, characterized in that.

7. In the first state, light from the display element is transmitted through the polarizer, transmitted through the second quarter-wave plate, and then split into a first reflected light that is reflected by the semi-transmissive reflective surface and a first transmitted light that is transmitted through the semi-transmissive reflective surface, and the first reflected light is transmitted through the second quarter-wave plate and absorbed by the polarizer, The first transmitted light passes through the first quarter-wave plate, is reflected by the polarization-selective semi-transmissive reflective element, passes through the first quarter-wave plate, is reflected by the semi-transmissive reflective surface, passes through the first quarter-wave plate, passes through the polarization-selective semi-transmissive reflective element, and is incident on the exit pupil. In the second state, The external light passes through the polarization-selective semi-transmissive reflective element, passes through the first quarter-wave plate, and then is split into a second transmitted light that passes through the semi-transmissive reflective surface and a second reflected light that is reflected by the semi-transmissive reflective surface. The second transmitted light passes through the second quarter-wave plate, passes through the polarizer, and is incident on the display element. The second reflected light passes through the first quarter-wave plate, is reflected by the polarization-selective semi-transmissive reflective element, passes through the first quarter-wave plate, passes through the semi-transmissive reflective surface, passes through the second quarter-wave plate, and is absorbed by the polarizer. The optical system according to claim 1 or 2, characterized in that.

8. A display element, An optical system including a polarization-selective semi-transmissive reflective element, a first quarter-wave plate, an optical member including a semi-transmissive reflective surface, a second quarter-wave plate, and a polarizer, which are arranged in order from the side of the exit pupil to the side of the display element, and guiding the light from the display element to the exit pupil. The optical system is characterized in that it can be changed between a first state in which the polarization directions of the polarization-selective semi-transmissive reflective element and the polarizer are orthogonal to each other and a second state in which the polarization directions of the polarization-selective semi-transmissive reflective element and the polarizer coincide. A display device.

9. The polarization-selective semi-transmissive reflective element reflects light in a first polarization direction and transmits light in a second polarization direction orthogonal to the first polarization direction. The polarizer transmits light in the first polarization direction and absorbs light in the second polarization direction in the first state, and absorbs light in the first polarization direction and transmits light in the second polarization direction in the second state. The display device according to claim 8, characterized in that.

10. In the second state, the polarizer absorbs light that passes through the semi-transmissive reflective surface of the external light and then passes through the semi-transmissive reflective surface after being reflected by the polarization-selective semi-transmissive reflective element. The display device according to claim 8 or 9, characterized in that.

11. The first quarter-wave plate and the second quarter-wave plate are arranged in a state where their slow axes are inclined by 90 degrees with respect to each other. The display device according to claim 8 or 9, wherein the second quarter-wave plate is arranged such that its slow axis is inclined by 45 degrees with respect to the polarization transmission axis of the polarizer.

12. The display device according to claim 8 or 9, wherein the optical system can be changed between the first state and the second state by rotating the polarizer by 90 degrees.

13. The polarizer is an element that utilizes the polarization characteristics of the liquid crystal, The optical system according to claim 8 or 9, wherein the optical system can be changed between the first state and the second state by changing the voltage application state to the polarizer.

14. In the first state, The light from the display element passes through the polarizer, passes through the second quarter-wave plate, and then is split into a first reflected light that is reflected by the semi-transmissive reflective surface and a first transmitted light that passes through the semi-transmissive reflective surface. The first reflected light passes through the second quarter-wave plate and is absorbed by the polarizer. The first transmitted light passes through the first quarter-wave plate, is reflected by the polarization-selective semi-transmissive reflective element, passes through the first quarter-wave plate, is reflected by the semi-transmissive reflective surface, passes through the first quarter-wave plate, passes through the polarization-selective semi-transmissive reflective element, and enters the exit pupil. In the second state, External light passes through the polarization-selective semi-transmissive reflective element, passes through the first quarter-wave plate, and then is split into a second transmitted light that passes through the semi-transmissive reflective surface and a second reflected light that is reflected by the semi-transmissive reflective surface. The second transmitted light passes through the second quarter-wave plate, passes through the polarizer, and enters the display element. The second reflected light passes through the first quarter-wave plate, is reflected by the polarization-selective semi-transmissive reflective element, passes through the first quarter-wave plate, passes through the semi-transmissive reflective surface, passes through the second quarter-wave plate, and is absorbed by the polarizer. The display device according to claim 8 or 9.

15. The display device according to claim 8 or 9, wherein the optical system changes between the first state and the second state according to the state of the display device.

16. The display device according to claim 8 or 9, wherein the optical system is in the first state when the power of the display device is ON, and is in the second state when the power of the display device is OFF.

17. When the optical system is in the first state and the posture of the display device is maintained for a predetermined time or longer in a state where the direction from the side of the display element to the side of the exit pupil is vertically upward, the optical system changes to the second state. The display device according to claim 8 or 9.

18. The display device according to claim 8 or 9, characterized in that it can be worn on the head of an observer.

19. A display element, A polarization-selective semi-transmissive reflective element, a first quarter-wave plate, an optical member including a semi-transmissive reflective surface, a second quarter-wave plate, and a polarizer, which are arranged in order from the side of the exit pupil to the side of the display element, and an optical system that guides light from the display element to the exit pupil. A control device for a display device having: When the display device is not in a predetermined state, the polarization direction of the polarizer is controlled so that the polarization directions of the polarization-selective semi-transmissive reflective element and the polarizer are orthogonal to each other in a first state. The control device is characterized in that when the display device is in the predetermined state, the polarization direction of the polarizer is controlled so that the polarization directions of the polarization-selective semi-transmissive reflective element and the polarizer coincide with each other in a second state.

20. The control device according to claim 19, wherein the predetermined state is a state in which the power supply of the display device is OFF or in a sleep mode.

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