Optical systems and display devices

Abstract

This invention provides an optical system that enables good image observation and gaze detection. [Solution] The optical system includes a first transmission reflective surface 21, a second transmission reflective surface 22, and an absorptive polarizer 11. At least a part of the optical system guides second wavelength light, which has a different wavelength range from the first wavelength light, incident from the observation side, to the imaging system. The transmittance of the first transmission reflective surface for the first and second linearly polarized first wavelength light is Tp11, Ts11; the transmittance of the first transmission reflective surface for the first and second linearly polarized second wavelength light is Tp12, Ts12; the transmittance of the absorptive polarizer for the third and fourth linearly polarized first wavelength light is Tp21, Ts21; and the transmittance of the absorptive polarizer for the third and fourth linearly polarized second wavelength light is Tp22, Ts22. In this case, Ts11 / Tp11≦0.1 and Ts21 / Tp21≦0.1 are satisfied, and at least one of Ts12 / Tp12≧0.5 and Ts22 / Tp22≧0.5 is satisfied.

Description

Technical Field

[0001] The present invention relates to an optical system suitable for a display device such as a head-mounted display (HMD).

Background Art

[0002] As such an optical system, a type that folds the optical path from the display element to the observer's eye (observation side) using two transmissive-reflective surfaces is used. Patent Document 1 discloses an optical system in which the transmissive-reflective surface on the display element side is a polarizing beam splitter and the transmissive-reflective surface on the observation side is a half mirror.

[0003] Further, Patent Document 2 discloses an HMD having an optical system that folds the optical path and an imaging system that images the observer's eye to perform gaze detection.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In an HMD having an imaging system, it is necessary to reduce ghosts caused by external light incident from the observation side and enable good gaze detection.

Means for Solving the Problems

[0006] An optical system, as one aspect of the present invention, guides first wavelength light from a display element to the observation side. The optical system includes a first transmission reflective surface that transmits first linearly polarized light and reflects second linearly polarized light having a different polarization direction from the first linearly polarized light; a second transmission reflective surface positioned on the observation side of the first transmission reflective surface, which transmits a portion of the incident light and reflects the other portion regardless of the polarization direction of the incident light; and an absorbing polarizer positioned on the observation side of the second transmission reflective surface, which transmits third linearly polarized light and absorbs fourth linearly polarized light having a different polarization direction from the third linearly polarized light. At least a part of the optical system guides second wavelength light, which has a different wavelength range from the first wavelength light and is incident from the observation side, to the imaging system. The transmittances of the first transmission reflective surface for first linearly polarized and second linearly polarized light of the first wavelength are Tp11 and Ts11, respectively, and the transmittances of the first transmission reflective surface for first linearly polarized and second linearly polarized light of the second wavelength are Tp12 and Ts12, respectively. Let Tp21 and Ts21 be the transmittances of the absorbing polarizer for the third and fourth linearly polarized light of the first wavelength, respectively, and Tp22 and Ts22 be the transmittances of the absorbing polarizer for the third and fourth linearly polarized light of the second wavelength, respectively. Ts11 / Tp11≦0.1 Ts21 / Tp21 ≤ 0.1 Both conditions must be satisfied, and Ts12 / Tp12≧0.5 Ts22 / Tp22≧0.5 The invention is characterized by satisfying at least one of the following conditions. Furthermore, a display device having the above-described optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an optical system that reduces ghosting caused by ambient light incident from the observation side, enabling good image observation and good line-of-sight detection. [Brief explanation of the drawing]

[0008] [Figure 1] A cross-sectional view showing the basic configuration of the optical system in the embodiment. [Figure 2]A diagram showing the polarization state and optical path in Arrangement Example 1 of the polarization element group in the embodiment. [Figure 3] A diagram showing the polarization state and optical path in Arrangement Example 2 of the polarization element group in the embodiment. [Figure 4] A diagram showing the spectral transmittance characteristics of the PBS and linear polarizer in the embodiment. [Figure 5] A diagram showing the configuration of the display device of Example 1. [Figure 6] A diagram showing the infrared optical path in Example 1. [Figure 7] A diagram showing the configuration of the display device of Example 2. [Figure 8] A diagram showing the infrared optical path in Example 2. [Figure 9] A diagram showing the infrared optical path in Example 3. [Figure 10] A diagram showing the configuration of the display device of Example 4. [Figure 11] A diagram showing the configuration of the display device of Example 5. [Figure 12] A diagram showing the optical system of the display device of Example 6. [Figure 13] A diagram showing the optical system of the display device of Example 7. [Figure 14] A diagram showing specific examples of the display devices of Examples 1 to 7. [Figure 15] A diagram showing other specific examples of the display devices of Examples 1 to 7.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the basic configuration of the display system of the display device of the embodiment. The display device is used as an electronic viewfinder (EVF) or the like provided in an imaging device such as a head-mounted display (HMD) or a digital camera.

[0010] The display system is composed of a display element 4 and an optical system 1 that guides light in the first wavelength range (hereinafter referred to as first wavelength light) from the display element 4 to the exit pupil (pupil plane) S on the observation side. An observer's eye is arranged near the exit pupil S.

[0011] The display element 4 is composed of an organic EL element or a liquid crystal element, forms an original image on the display surface 41, and emits image light as the first wavelength light corresponding to the original image from the display surface 41. The display surface 41 is covered by a cover glass or other flat plate portion 42 composed of a parallel flat plate having no refractive power.

[0012] The optical system 1 has a lens element 100 composed of a plano-concave lens 101 and a plano-convex lens 102 arranged in order from the display element side. The plano-concave lens 101 and the plano-convex lens 102 are formed of the same medium and are joined to each other.

[0013] The optical system 1 also has a polarization element group 20 for forming a triple path as a folded optical path. The polarization element group 20 includes a first transmission-reflection surface 21, a first λ / 4 phase plate 31, a second transmission-reflection surface 22, a second λ / 4 phase plate 32, and a linear polarizer 11 arranged in order from the display element side to the observation side.

[0014] The first transmission-reflection surface 21 is a polarization beam splitter (PBS) as a reflective polarizer having polarization selectivity, which transmits the first linearly polarized light of the incident light and reflects the second linearly polarized light (orthogonal) having a polarization direction different from that of the first linearly polarized light. In the following description, the first transmission-reflection surface 21 is referred to as PBS21. PBS21 is formed on at least one of the curved surfaces (joint surfaces) of the plano-concave lens 101 and the plano-convex lens 102.

[0015] The second transmission-reflection surface 22 is a half mirror that transmits a part of the incident light regardless of the polarization direction and wavelength of the incident light and reflects the other part. In the following description, the second transmission-reflection surface 22 is referred to as half mirror 22. The half mirror 22 is formed between the first λ / 4 phase plate 31 and the second λ / 4 phase plate 32 and joined to them. Note that the transmittance and reflectance of the half mirror 22 do not necessarily have to be 50%:50%.

[0016] The first λ / 4 phase element 31 is joined to the observation-side plane of the plano-convex lens 102, and the second λ / 4 phase element 32 is joined to the linear polarizer 11.

[0017] The linear polarizer 11 is an absorbing polarizer that transmits the third linearly polarized light in the incident light and absorbs the fourth linearly polarized light, which has a different polarization direction (orthogonal) to the third linearly polarized light. In this embodiment, the third linearly polarized light has the same polarization direction as the second linearly polarized light, and the fourth linearly polarized light has the same polarization direction as the first linearly polarized light. The linear polarizer 11 is joined to the observation-side plane of the second λ / 4 phase element 32. In this way, the optical system 1 is configured as a single optical component, which facilitates positional adjustment between the optical system 1 and the display element 4.

[0018] Furthermore, the PBS21 and the linear polarizer 11 are positioned so that their transmission axes are parallel (same) or perpendicular to each other. The first λ / 4 phase element 31 and the second λ / 4 phase element 32 are positioned so that their slow phase axes are parallel or perpendicular to each other. Depending on the combination of these transmission axis and slow phase axis orientations, the third and fourth linearly polarized light will have the same polarization direction as the first and second linearly polarized light, or the same polarization direction as the second and first linearly polarized light.

[0019] In the optical system 1 having the basic configuration described above, the first wavelength light emitted from the display surface 41 passes through the flat plate portion 42 and enters the optical system 1 from the plane on the display element side of the plano-concave lens 101. Of the first wavelength light that has passed through the plano-concave lens 101, the first linearly polarized light passes through the PBS 21 and enters the plano-convex lens 102. A portion of the first wavelength light as circularly polarized light that has passed through the plano-convex lens 102 and the first λ / 4 phase element 31 is reflected by the half mirror 22, passes through the first λ / 4 phase element 31 again and is converted to second linearly polarized light. Then, the first wavelength light as second linearly polarized light passes through the plano-convex lens 102, is reflected by the PBS 21, passes through the plano-convex lens 102 and the first λ / 4 phase element 31 again and is converted to circularly polarized light before entering the half mirror 22. The first wavelength light, as circularly polarized light transmitted through the half-mirror 22, is converted to third linear polarization by the second λ / 4 phase element 32, then transmitted through the linear polarizer 11 and reaches the exit pupil S.

[0020] Next, we will describe the polarization state and optical path of the first wavelength light in specific arrangement examples 1 and 2 of the polarization element group 20 in the optical system 1. Here, both the first transmission / reflection surface (PBS) 21 and the linear polarizer 11 are assumed to have ideal polarization characteristics. Also, the plano-concave lens 101 and the plano-convex lens 102 are not shown in the illustration.

[0021] [Layout example 1] Figure 2(A) shows the polarization state and optical path of the image light as the first wavelength light in arrangement example 1. As shown at the bottom of the figure, the direction of the transmission axis of PBS21 (i.e., the polarization direction of the first linear polarization) and the direction of the transmission axis of the linear polarizer 11 are orthogonal to each other. In addition, the direction of the slow axis of the first λ / 4 phase element 31 and the direction of the slow axis of the second λ / 4 phase element 32 are orthogonal to each other, with inclinations of +45° and -45°, respectively, with respect to the polarization direction of the first linear polarization when viewed from the observation side. The following right-handed and left-handed circular polarizations refer to right-handed and left-handed circular polarizations when viewed in the direction of light propagation. When viewed in the direction of light propagation, if the light is traveling toward the display element side (right side in the figure), it is the direction of rotation when observed from the display element side facing the pupil S, and if the light is traveling toward the pupil side (left side in the figure), it is the direction of rotation when observed from the pupil side facing the display element side.

[0022] Image light from the display surface 41 of the display element 4 passes through the flat plate portion 42 and is incident on the polarization element portion 20 of the optical system 1. Of the image light, the first linearly polarized light passes through the PBS 21 and is converted to right-handed circularly polarized light while passing through the first λ / 4 phase element 31. A portion of the right-handed circularly polarized light passes through the half mirror 22 and is converted to a fourth linearly polarized light with the same polarization direction as the first linearly polarized light while passing through the second λ / 4 phase element 32. The fourth linearly polarized light is absorbed by the linear polarizer 11.

[0023] On the other hand, some of the right-handed circularly polarized light from the first λ / 4 phase element 31 is reflected by the half mirror 22 and becomes left-handed circularly polarized light. The left-handed circularly polarized light is converted to second linearly polarized light while passing through the first λ / 4 phase element 31 again. The second linearly polarized light reflected by PBS 21 is converted to left-handed circularly polarized light while passing through the first λ / 4 phase element 31 again. The left-handed circularly polarized light passes through the half mirror 22 and passes through the second λ / 4 phase element 32 and is converted to third linearly polarized light with the same polarization direction as the second linearly polarized light. The third linearly polarized light passes through the linear polarizer 11 and reaches the exit pupil S.

[0024] Figure 2(B) shows the polarization state and optical path of ambient light (ghost light) as the first wavelength light incident from the observation side in arrangement example 1. Of the ambient light incident from the observation side into the optical system 1, the fourth linearly polarized light with the same polarization direction as the first linearly polarized light is absorbed by the linear polarizer 11. Also, of the ambient light, the third linearly polarized light with the same polarization direction as the second linearly polarized light is transmitted through the linear polarizer 11 and converted to left-handed circularly polarized light while being transmitted through the second λ / 4 phase element 32. The light reflected by the half mirror 22 from the left-handed circularly polarized light becomes right-handed circularly polarized light and is converted to the fourth linearly polarized light while being transmitted through the second λ / 4 phase element 32. The fourth linearly polarized light returns to the linear polarizer 11 and is absorbed.

[0025] On the other hand, the left-handed circularly polarized light transmitted through the half-mirror 22 is converted to second linearly polarized light while being transmitted through the first λ / 4 phase element 31. The second linearly polarized light is reflected by the PBS 21 and converted back to left-handed circularly polarized light while being transmitted again through the first λ / 4 phase element 31. The left-handed circularly polarized light that has been transmitted through the half-mirror 22 is converted back to first linearly polarized light while being transmitted again through the second λ / 4 phase element 32. The first linearly polarized light is transmitted through the PBS 21 and the flat plate portion 42 and reaches the display surface 41. In addition, some of the left-handed circularly polarized light is reflected by the half-mirror 22 and becomes right-handed circularly polarized light, and this right-handed circularly polarized light is converted back to second linearly polarized light while being transmitted through the first λ / 4 phase element 31. The second linearly polarized light is reflected by the PBS 21 and converted back to left-handed circularly polarized light while being transmitted again through the first λ / 4 phase element 31. The left-handed circularly polarized light that has been transmitted through the half-mirror 22 is converted back to third linearly polarized light while being transmitted again through the second λ / 4 phase element 32. The third linearly polarized light passes through the linear polarizer 11 and is directed toward the observation side.

[0026] Furthermore, the left-handed circularly polarized light converted from the second linearly polarized light by the first λ / 4 phase element 31 is reflected by the half mirror 22 to become right-handed circularly polarized light. The right-handed circularly polarized light is then transmitted back through the first λ / 4 phase element 31 and polarized to the first linearly polarized light. The first linearly polarized light passes through the PBS 21 and the flat plate portion 42 to reach the display surface 41.

[0027] Based on the above, the only ambient light that may be guided to the observation side by the optical system 1 is the ambient light that has been reflected once by PBS21.

[0028] [Layout example 2] Figure 3(A) shows the polarization state and optical path of the image light as the first wavelength light in arrangement example 1. As shown at the bottom of the figure, the orientation of the transmission axis of PBS21 (the polarization direction of the first linear polarization) and the orientation of the transmission axis of the linear polarizer 11 are parallel to each other. Also, the orientation of the slow axis of the first λ / 4 phase element 31 and the orientation of the slow axis of the second λ / 4 phase element 32 are both tilted at +45° with respect to the polarization direction of the first linear polarization when viewed from the observation side, and are parallel to each other. The right-handed and left-handed circular polarizations below refer to the right-handed and left-handed circular polarizations when viewed in the direction of light propagation.

[0029] Image light from the display surface 41 of the display element 4 passes through the flat plate portion 42 and enters the polarization element portion 20 of the optical system 1. Of the image light, the first linearly polarized light passes through the PBS 21 and is converted to right-handed circularly polarized light while passing through the first λ / 4 phase element 31. A portion of the right-handed circularly polarized light passes through the half mirror 22 and is converted to a fourth linearly polarized light with the same polarization direction as the second linearly polarized light by passing through the second λ / 4 phase element 32. The fourth linearly polarized light is absorbed by the linear polarizer 11.

[0030] On the other hand, some of the right-handed circularly polarized light is reflected by the half-mirror 22 and becomes left-handed circularly polarized light. The left-handed circularly polarized light is transmitted again through the first λ / 4 phase element 31 and converted into second linearly polarized light. The second linearly polarized light reflected by PBS 21 is transmitted again through the first λ / 4 phase element 31 and converted into left-handed circularly polarized light. The left-handed circularly polarized light is transmitted through the half-mirror 22 and through the second λ / 4 phase element 32 and converted into third linearly polarized light with the same polarization direction as the first linearly polarized light. The third linearly polarized light is transmitted through the linear polarizer 11 and reaches the exit pupil S.

[0031] Figure 3(B) shows the polarization state and optical path of ambient light (ghost light) as the first wavelength light incident from the observation side in arrangement example 2. Of the ambient light incident from the observation side into the optical system 1, the fourth linearly polarized light with the same polarization direction as the second linearly polarized light is absorbed by the linear polarizer 11. Also, the third linearly polarized light of the ambient light with the same polarization direction as the first linearly polarized light is transmitted through the linear polarizer 11 and the second λ / 4 phase element 32 and converted to left-handed circularly polarized light. The light reflected by the half mirror 22 from the left-handed circularly polarized light becomes right-handed circularly polarized light and is transmitted through the second λ / 4 phase element 32 and converted to the fourth linearly polarized light. The fourth linearly polarized light returns to the linear polarizer 11 and is absorbed.

[0032] On the other hand, the left-handed circularly polarized light transmitted through the half-mirror 22 is transmitted through the first λ / 4 phase element 31 and converted to second linearly polarized light. The second linearly polarized light is reflected by the PBS 21 and transmitted again through the first λ / 4 phase element 31 and converted to left-handed circularly polarized light. The light of the left-handed circularly polarized light that has been transmitted through the half-mirror 22 is transmitted again through the second λ / 4 phase element 32 and converted to first linearly polarized light. The first linearly polarized light is transmitted through the PBS 21 and the flat plate portion 42 and reaches the display surface 41. In addition, some of the left-handed circularly polarized light is reflected by the half-mirror 22 and becomes right-handed circularly polarized light, and this right-handed circularly polarized light is transmitted through the first λ / 4 phase element 31 and converted to second linearly polarized light. The second linearly polarized light is reflected by the PBS 21 and transmitted again through the first λ / 4 phase element 31 and converted to left-handed circularly polarized light. The light of the left-handed circularly polarized light that has been transmitted through the half-mirror 22 is transmitted again through the second λ / 4 phase element 32 and converted to third linearly polarized light. The third linearly polarized light passes through the linear polarizer 11 and is directed toward the observation side.

[0033] Furthermore, the left-handed circularly polarized light converted from the second linearly polarized light by the first λ / 4 phase element 31 is reflected by the half mirror 22 to become right-handed circularly polarized light. The right-handed circularly polarized light is then transmitted back through the first λ / 4 phase element 31 and polarized to the first linearly polarized light. The first linearly polarized light is transmitted through the PBS 21 and the flat plate portion 42 to reach the display surface 41.

[0034] Based on the above, the only ambient light that may be guided to the observation side by the optical system 1 is the ambient light that has been reflected once by PBS21.

[0035] In the arrangement examples 1 and 2 described above, the optical path for displaying the image light is as follows: display element 4 → PBS21 (transmitted) → half mirror 22 (reflected) → PBS21 (reflected) → half mirror 22 (transmitted) → linear polarizer 11 (transmitted) → exit pupil S. On the other hand, the first optical path of ambient light from the observation side is as follows: linear polarizer 11 (transmitted) → half mirror 22 (transmitted) → PBS21 (reflected) → half mirror 22 (transmitted) → linear polarizer 11 (transmitted) → exit pupil S. The second optical path of ambient light is as follows: linear polarizer 11 (transmitted) → half mirror 22 (transmitted) → PBS21 (reflected) → half mirror 22 (reflected) → PBS21 (transmitted) → display element 4.

[0036] In the optical system disclosed in Patent Document 2, the optical path of ambient light from the observation side is an optical path that is reflected twice by the PBS 21. In contrast, in this embodiment, the optical path of ambient light from the observation side is an optical path that is reflected only once by the PBS (first transmission reflective surface) 21. As a result, in this embodiment, the generation of ghosting caused by ambient light incident from the observation side can be suppressed.

[0037] In the optical system of the embodiment, one of the PBS21 and the half mirror22 is formed in a curved shape and acts as a reflective surface A having light-gathering power. When the focal length at the reflection at reflective surface A is fA, and the air-equivalent optical path length from the reflection at reflective surface A to the exit pupil S is LaA, the optical system of the embodiment satisfies the following condition (1).

[0038] 1 <LaA / fA≦2.5 (1) By satisfying this condition, external light reflected only once by PBS21 is less likely to reach the exit pupil S, thereby suppressing the occurrence of ghosting.

[0039] Furthermore, if PBS21 is made into a concave surface with a concave shape towards the observation side as the reflective surface A, it is advantageous for miniaturizing (reducing the diameter of) the optical system, and therefore preferable.

[0040] In this embodiment, PBS21 reflects linearly polarized light perpendicular to the transmission axis, and the linear polarizer 11 absorbs linearly polarized light perpendicular to the transmission axis. However, the spectral characteristics of the transmittance of these polarizers can be discussed similarly. For this reason, the spectral transmittance characteristics of PBS21 and the linear polarizer 11 are defined as follows. Note that a polarizer whose transmittance for linearly polarized light in the infrared wavelength range perpendicular to the transmission axis (hereinafter referred to as S-polarization for convenience) is significantly higher than its transmittance for S-polarization in the visible wavelength range is called an infrared-infrared-infrared polarizer. In this infrared-infrared-infrared polarizer, the transmittance for linearly polarized light in the infrared wavelength range parallel to the transmission axis (hereinafter referred to as P-polarization for convenience) is equivalent to the transmittance for P-polarization in the visible wavelength range. A polarizer whose transmittance for S-polarization and P-polarization in the infrared wavelength range is equivalent to the transmittance for S-polarization and P-polarization in the visible wavelength range is called an infrared-compatible polarizer. In this infrared polarizer, the transmittance for S-polarized light in the infrared and visible wavelength ranges is significantly lower than the transmittance for P-polarized light.

[0041] Figure 4(A) shows the spectral transmittance characteristics of PBS21 and linear polarizer 11 without infrared support, and Figure 4(B) shows the spectral transmittance characteristics of PBS21 and linear polarizer 11 with infrared support. In these figures, the horizontal axis is wavelength λ, with the left side of the vertical dashed line representing the visible wavelength range and the right side representing the infrared wavelength range. The vertical axis is the transmittance T of each polarizer. The solid line shows the transmittance of each polarizer for linearly polarized light (first and third linearly polarized light as P-polarization) in a polarization direction parallel to the transmission axis, and the dashed line shows the transmittance of each polarizer for linearly polarized light (second and fourth linearly polarized light as S-polarization) in a polarization direction perpendicular to the transmission axis.

[0042] Let Tp11 and Ts11 be the transmittances of PBS21 for the first linearly polarized and second linearly polarized light of the first wavelength in the visible wavelength range, respectively. Let Tp12 and Ts12 be the transmittances of PBS21 for the first linearly polarized and second linearly polarized light of the second wavelength in the infrared wavelength range, respectively. Let Tp21 and Ts21 be the transmittances of the linear polarizer 11 for the third linearly polarized and fourth linearly polarized light of the first wavelength range, respectively. Let Tp22 and Ts22 be the transmittances of the linear polarizer 11 for the third linearly polarized and fourth linearly polarized light of the second wavelength range, respectively. Note that in Figures 4(A) and (B), Tp11 and Tp21, Ts11 and Ts21, Tp12 and Tp22, and Ts12 and Ts22 are shown as being the same, but in reality, they may be the same or different in transmittance.

[0043] In the visible wavelength range, with PBS21 (non-infrared compatible) and linear polarizer 11 (infrared compatible), Tp11, Tp21 = 1 Ts11, Ts21 = 0 That would be ideal, and at least, Ts11 / Tp11≦0.1 Ts21 / Tp21 ≤ 0.1 It is sufficient to satisfy the conditions.

[0044] In the infrared wavelength range, with PBS21 and linear polarizer 11 which are not infrared compatible, Tp12, Tp22 = 1 Ts12, Ts22 = 1 That would be ideal, and at least, Ts12 / Tp12≧0.5 Ts22 / Tp22≧0.5 It is sufficient to satisfy the following conditions. Ts12 / Tp12≧0.8 Ts22 / Tp22≧0.8 If so, that would be preferable. Ts12 / Tp12≧0.9 Ts22 / Tp22≧0.9 That would be even better.

[0045] In the infrared wavelength range, with the infrared-compatible PBS21 and linear polarizer 11, Tp12, Tp22 = 1 Ts12, Ts22 = 0 That would be ideal, and at least, Ts12 / Tp12<0.5 Ts22 / Tp22<0.5 It is sufficient to satisfy the following conditions. Ts12 / Tp12 ≤ 0.2 Ts22 / Tp22 ≤ 0.2 If so, that would be preferable. Ts12 / Tp12 ≤ 0.1 Ts22 / Tp22 ≤ 0.1 That would be even better.

[0046] The optical system 1 of the embodiment is Ts11 / Tp11≦0.1 (2) Ts21 / Tp21 ≤ 0.1 (3) Both conditions must be satisfied, and Ts12 / Tp12≧0.5 (4) Ts22 / Tp22≧0.5 (5) It satisfies at least one of the following conditions.

[0047] When reflective polarizers such as PBS21 are constructed from dielectric multilayer films, in order to achieve infrared compatibility as shown in Figure 4(B), it is necessary to increase the number of multilayer layers compared to the case where infrared compatibility is not achieved as shown in Figure 4(A), resulting in increased manufacturing costs. In this respect, when reflective polarizers are constructed from wire grids, the short-wavelength range that can be handled is determined by the grid pitch, and longer wavelengths basically function as infrared-compatible polarizers as shown in Figure 4(B). Wire grid reflective polarizers have a wide wavelength range and low dependence on the incident angle, making it easy to obtain high contrast in the direction of the transmission axis and in the direction perpendicular to it (making it easy to achieve a high extinction ratio).

[0048] Furthermore, in a transmissive polarizer such as the linear polarizer 11, obtaining the characteristics shown in Figure 4(B) from the characteristics shown in Figure 4(A) requires extending the wavelength range of linearly polarized light that can be absorbed to the infrared region, which increases manufacturing costs.

[0049] From the above, it is not necessarily required to satisfy both equations (4) and (5); it is sufficient to satisfy at least one of them. [Examples]

[0050] Figure 5 shows the configuration of the display device of Example 1. This display device has a configuration that adds an imaging unit 5, an infrared light source 6, and a linear polarizer 7 for the light source to the display system shown in Figure 1.

[0051] The imaging unit 5 includes an imaging optical system 51 and an image sensor 52. The infrared light source 6 irradiates the observation side with second wavelength light in the infrared wavelength range without passing through the optical system 1. The linear polarizer 7 is an absorbing polarizer that transmits linearly polarized light from the infrared light source 6 with a polarization direction parallel to the transmission axis (having the same polarization direction as the fourth linearly polarized light) and absorbs linearly polarized light with a polarization direction perpendicular to the transmission axis (having the same polarization direction as the third linearly polarized light).

[0052] The second wavelength light emitted from the infrared light source 6 and transmitted through the linear polarizer 7 is reflected by the observer's eye (pupil) positioned near the exit pupil S of the optical system 1 and enters the optical system 1 from the observation side. The second wavelength light that has passed through the optical system 1 then enters the imaging unit 5. The imaging unit 5 acquires information about the eye by capturing the pupil image formed by the imaging optical system 51 with the image sensor 52.

[0053] Figure 6 shows the optical path of the second wavelength light in this embodiment. The arrangement of the optical system 1 in this embodiment is the same as arrangement example 1 shown in Figures 2(A) and (B). However, the same arrangement as arrangement example 2 shown in Figures 3(A) and (B) may be adopted, and in this case the optical path of the second wavelength light will also be the same. Hereinafter, the optical path will be described assuming that the PBS21 and the linear polarizer 11 each have the ideal spectral transmittance characteristics described above for the second wavelength light. In this embodiment, the PBS21 is shown with a solid line in the figure as infrared-compatible, and the linear polarizer 11 is shown with a dashed line in the figure as non-infrared-compatible. The infrared-compatible PBS21 can be constructed with a wire grid, and in this case, a high extinction ratio can be obtained even when the incident angle range of the image light on the PBS21 is large. As a result, a high-contrast image can be displayed.

[0054] The second wavelength light incident on the optical system 1 from the observation side passes through the linear polarizer 11 regardless of its polarization direction. The third linearly polarized light (which has the same polarization direction as the second linearly polarized light) that has passed through the linear polarizer 11 follows an optical path similar to that of the third linearly polarized ambient light shown in Figure 2(B), undergoing a polarization state transformation and heading towards the observation side or display element side. The fourth linearly polarized light, which was incident on the optical system 1 as the third linearly polarized light and returned to the linear polarizer 11, exits the optical system 1 without being absorbed by the linear polarizer 11 and returns to the observation side.

[0055] Furthermore, the fourth linearly polarized light of the second wavelength (having the same polarization direction as the first linearly polarized light) that has passed through the linear polarizer 11 passes through the second λ / 4 phase element 32 and is converted to right-handed circularly polarized light. A portion of this right-handed circularly polarized light is reflected by the half mirror 22 and becomes left-handed circularly polarized light. This left-handed circularly polarized light is then converted to third linearly polarized light by passing through the second λ / 4 phase element 32 again. This third linearly polarized light is not absorbed by the linear polarizer 11 and exits the optical system 1, returning to the observation side.

[0056] Meanwhile, the right-handed circularly polarized light transmitted through the half-mirror 22 is converted to first linearly polarized light by passing through the first λ / 4 phase element 31. The first linearly polarized light passes through the PBS 21 and exits the optical system 1, heading towards the display element.

[0057] In this way, the second wavelength light incident on the optical system 1 from the observation side as fourth linear polarization passes through the half mirror 22 and PBS 21 once each before heading towards the display element. This enables good line-of-sight detection through the imaging unit 5 located on the display element side.

[0058] In this embodiment, the optical system 1 acts as a flat plate with no refractive power for second-wavelength light incident on the imaging unit 5 from the observation side. Therefore, a general-purpose infrared camera can be used as the imaging unit 5, and as a result, a display device that can perform good gaze detection at low cost can be provided. Furthermore, by configuring the imaging unit 5 to capture the pupil image via the optical system 1, the entire display device can be miniaturized. In addition, since the imaging unit 5 can be positioned at an inclination angle smaller than the maximum display field of view, capturing the pupil image (i.e., gaze detection) becomes easier.

[0059] In this embodiment, we have described a case where one infrared light source 6 and one imaging unit 5 are provided for one optical system 1, but the number of infrared light sources and imaging units may be multiple. This is also true for other embodiments described later. [Examples]

[0060] Figure 7 shows the configuration of the display device of Example 2. This display device has a configuration that adds an imaging unit 5 and an infrared light source 6 to the display system shown in Figure 1.

[0061] The imaging unit 5 includes an imaging optical system 51 and an image sensor 52. The infrared light source 6 irradiates the observation side with second wavelength light in the infrared wavelength range via the optical system 1. In this embodiment, the second wavelength light from the infrared light source 6 is irradiated to the observation side via the entire optical system 1, but it is sufficient if it is irradiated to the observation side via at least a part of the optical system 1.

[0062] The second wavelength light emitted from the infrared light source 6 and transmitted through the optical system 1 from the display element side is reflected by the observer's eye (pupil) positioned near the exit pupil S of the optical system 1 and enters the optical system 1 from the observation side. The second wavelength light that has passed through the optical system 1 then enters the imaging unit 5. The imaging unit 5 acquires information about the eye by capturing the pupil image formed by the imaging optical system 51 with the image sensor 52.

[0063] Figures 8(A) and 8(B) show the polarization state and optical path of the second wavelength light in this embodiment. The arrangement of the optical system 1 in this embodiment is the same as arrangement example 1 shown in Figures 2(A) and 2(B). However, the same arrangement as arrangement example 2 shown in Figures 3(A) and 3(B) may also be adopted, in which case the optical path of the second wavelength light will be the same. Hereinafter, the optical path will be described assuming that the PBS21 and the linear polarizer 11 each have the ideal spectral transmittance characteristics described above for the second wavelength light. In this embodiment, the PBS21 is shown with a dashed line in the figure as being incompatible with infrared, and the linear polarizer 11 is shown with a solid line in the figure as being compatible with infrared.

[0064] Figure 8(A) shows the polarization state and optical path of the second wavelength light emitted from the infrared light source 6 and incident on the optical system 1 from the display element side. The second wavelength light emitted from the infrared light source 6 passes through the PBS 21, which is not infrared compatible, regardless of its polarization direction. Of the second wavelength light that has passed through the PBS 21, the second linearly polarized light passes through the first λ / 4 phase element 31 and is converted to left-handed circular polarization. A portion of the left-handed circular polarization passes through the half mirror 22 and the second λ / 4 phase element 32 and is converted to third linearly polarized light (which has the same polarization direction as the second linearly polarized light). The third linearly polarized light passes through the linear polarizer 11 and exits the optical system 1, heading towards the observation side.

[0065] Furthermore, a portion of the left-handed circularly polarized light from the first λ / 4 phase element 31 is reflected by the half-mirror 22 and becomes right-handed circularly polarized light. This right-handed circularly polarized light then passes through the first λ / 4 phase element 31 again and is converted back into first linearly polarized light. The first linearly polarized light passes through the PBS 21 and exits the optical system 1, returning to the display element side.

[0066] Meanwhile, the first linearly polarized light of the second wavelength transmitted through PBS21 is transmitted through the first λ / 4 phase element 31 and converted to right-handed circularly polarized light. A portion of the right-handed circularly polarized light is transmitted through the half mirror 22 and the second λ / 4 phase element 32 and converted to fourth linearly polarized light (having the same polarization direction as the first linearly polarized light) and absorbed by the linear polarizer 11.

[0067] Furthermore, a portion of the right-handed circularly polarized light from the first λ / 4 phase element 31 is reflected by the half-mirror 22 and becomes left-handed circularly polarized light. This left-handed circularly polarized light then passes through the first λ / 4 phase element 31 again and is converted into second linearly polarized light. The second linearly polarized light passes through the PBS 21 and exits the optical system 1, returning to the display element side.

[0068] In this way, of the second wavelength light incident on the optical system 1 from the display element side, the light component that passes through the PBS 21 and the half mirror 22 once each, and then passes through the linear polarizer 11, is directed towards the observation side.

[0069] Figure 8(B) shows the polarization state and optical path of the second wavelength light that is reflected by the observer's eye and incident on the optical system 1 from the observation side.

[0070] Of the second wavelength light incident on the optical system 1 from the observation side, the fourth linearly polarized light is absorbed by the linear polarizer 11, while the third linearly polarized light is transmitted through the linear polarizer 11. The third linearly polarized light transmitted through the linear polarizer 11 is transmitted through the second λ / 4 phase element 32 and converted to left-handed circularly polarized light. A portion of this left-handed circularly polarized light is reflected by the half mirror 22 and becomes right-handed circularly polarized light. The right-handed circularly polarized light is again transmitted through the second λ / 4 phase element 32 and converted to fourth linearly polarized light, which is absorbed by the linear polarizer 11. Therefore, the second wavelength light incident on the optical system 1 from the observation side does not return from the optical system 1 to the observation side.

[0071] Furthermore, the left-handed circularly polarized light transmitted through the half-mirror 22 is converted to second-order linearly polarized light by passing through the first λ / 4 phase element 31, but regardless of the polarization direction, it passes through the PBS 21 and exits the optical system 1, heading towards the display element.

[0072] In this way, the light component of the second wavelength light from the infrared light source 6 that was not reflected within the optical system 1 is irradiated to the observer's eye. Then, the light component of the second wavelength light that was reflected by the eye and not reflected within the optical system 1 reaches the imaging unit 5. This enables accurate line-of-sight detection through the imaging unit 5 located on the display element side.

[0073] In this embodiment, second-wavelength light emitted from the infrared light source 6 passes through the optical system 1 and irradiates the observation side, and the second-wavelength light reflected by the eye on the observation side passes through the optical system 1 and enters the imaging unit 5. Therefore, a general-purpose infrared camera can be used as the imaging unit 5, and a display device that can perform good line-of-sight detection at low cost can be provided. In addition, the entire display device can be made smaller compared to Embodiment 1.

[0074] In this embodiment, as described above, no reflected light returns to the observer side from the second wavelength light incident on the optical system 1 from the observer side. When using the corneal image formed by the second wavelength light reflected by the cornea for gaze detection, if the observer is wearing glasses and there is reflected light, the light reflected multiple times between the reflected light and the glasses may reach near the corneal image and interfere with gaze detection. In this embodiment, by avoiding the generation of such reflected light, gaze detection using the corneal image can be performed well. [Examples]

[0075] Figures 9(A) and (B) show the configuration of the display device of Example 3. This display device has the same configuration as the display device of Example 2. However, in this example, both the PBS21 and the linear polarizer 11 are shown as non-infrared compatible with dashed lines in the figure. In this example as well, the optical path will be described assuming that the PBS21 and the linear polarizer 11 each have the ideal spectral transmittance characteristics described above for second wavelength light.

[0076] Figure 9(A) shows the polarization state and optical path of the second wavelength light emitted from the infrared light source 6 and incident on the optical system 1 from the display element side. In Embodiment 2 shown in Figure 8(A), the first linear polarization of the second wavelength light incident on the optical system 1 from the infrared light source 6 and transmitted through PBS 21 is transmitted through the first λ / 4 phase element 31, the half mirror 22, and the second λ / 4 phase element 32, converted to fourth linear polarization, and absorbed by the linear polarizer 11. In contrast, in this embodiment, the first linear polarization of the second wavelength light incident on the optical system 1 from the infrared light source 6 and transmitted through PBS 21 is transmitted through the first λ / 4 phase element 31, the half mirror 22, and the second λ / 4 phase element 32, converted to fourth linear polarization, but is not absorbed by the linear polarizer 11 and is directed towards the observation side.

[0077] The optical path of the second-wavelength light with second linear polarization that enters the optical system 1 from the infrared light source 6 and passes through PBS 21 is the same as in Example 2.

[0078] In this embodiment, as in Embodiment 2, the second wavelength light incident on the optical system 1 from the display element side passes through the PBS 21 and the half mirror 22 once each, and the light component that passes through the linear polarizer 11 is directed towards the observation side.

[0079] Figure 9(B) shows the polarization state and optical path of the second wavelength light that is reflected by the observer's eye and incident on the optical system 1 from the observation side.

[0080] The second wavelength light incident on the optical system 1 from the observation side passes through the linear polarizer 11 regardless of its polarization direction. In Embodiment 2 shown in Figure 8(B), the third linear polarization of the second wavelength light that has passed through the linear polarizer 11 passes through the second λ / 4 phase element 32, is partially reflected by the half mirror 22, passes through the second λ / 4 phase element 32 again to be converted to fourth linear polarization and absorbed by the linear polarizer 11. In contrast, in this embodiment, the third linear polarization of the second wavelength light that has passed through the linear polarizer 11 passes through the second λ / 4 phase element 32, is partially reflected by the half mirror 22, passes through the second λ / 4 phase element 32 again to be converted to fourth linear polarization, but returns to the observation side without being absorbed by the linear polarizer 11.

[0081] The second linearly polarized light, transmitted through the half-mirror 22 and emitted from the first λ / 4 phase element 31, is emitted from the optical system 1 via the PBS 21, similar to Example 2, and heads towards the display element.

[0082] On the other hand, the fourth linear polarization of the second wavelength light that has passed through the linear polarizer 11 is converted to right-handed circular polarization by passing through the second λ / 4 phase element 32. A portion of the right-handed circular polarization is reflected by the half mirror 22 and becomes left-handed circular polarization, which is then converted to third linear polarization by passing through the second λ / 4 phase element 32 again and returning to the observation side through the linear polarizer 11.

[0083] Furthermore, the right-handed circularly polarized light transmitted through the half-mirror 22 is converted to first linearly polarized light by passing through the first λ / 4 phase element 31. The first linearly polarized light passes through PBS 21 and exits the optical system 1, heading towards the observation side.

[0084] In this way, the light component of the second wavelength light from the infrared light source 6 that is not reflected within the optical system 1 and passes through the linear polarizer 11 (unpolarized light) is irradiated to the observer's eye. Then, the light component of the second wavelength light that is reflected by the eye and not reflected within the optical system 1 reaches the imaging unit 5. This enables good line-of-sight detection through the imaging unit 5 located on the display element side.

[0085] In this embodiment, as in Embodiment 2, the second wavelength light emitted from the infrared light source 6 passes through the optical system 1 and irradiates the observation side, and the second wavelength light reflected by the eye on the observation side passes through the optical system 1 and enters the imaging unit 5. Therefore, a general-purpose infrared camera can be used as the imaging unit 5, and a display device that can perform good line-of-sight detection at low cost can be provided. In addition, the entire display device can be made smaller compared to Embodiment 1.

[0086] Furthermore, in this embodiment, all of the second-wavelength light transmitted through the half-mirror 22 can be used as illumination light for the observer's eyes and imaging light for the imaging unit 5, thus providing a display device with high utilization efficiency of the second-wavelength light emitted from the infrared light source 6. [Examples]

[0087] Figure 10 shows the configuration of the display device of Example 4. The basic configuration of this example is the same as that of Example 1. In this example, an absorbing polarizer 12 having a transmission axis in the same direction as the transmission axis of the PBS 21 is placed between the PBS 21 and the display element 4.

[0088] With this configuration, unwanted components (second linear polarization) in the first wavelength light incident from the display element 4 to the PBS21 can be reduced before it enters the PBS21, thus reducing the amount of unwanted components that may be present in the first wavelength light transmitted through the PBS21. This further enhances the contrast of the image displayed by the first wavelength light transmitted through the PBS21. [Examples]

[0089] Figure 11 shows the configuration of the display device of Example 5. The basic configuration of this example is the same as that of Example 4. In this example, a λ / 4 phase element 33 is placed between the absorbing polarizer 12 and the display element 4, with the slow axis tilted by ±45° with respect to the transmission axis of the absorbing polarizer 12, as described in Example 4.

[0090] This configuration makes it possible to suppress the stray light that results from the slight amount of first linearly polarized light reflected by PBS21 being reflected by the display element 4. [Examples]

[0091] Figure 12 shows the configuration of the optical system 1 of the display device in Example 6. In Examples 1 to 5, the lens section 100 was constructed by joining a plano-concave lens 101 and a plano-convex lens 102, and the mirror 22 was formed in a planar shape and the PBS 21 in a curved shape. In contrast, in this example, the lens section 100A is constructed by joining a plano-convex lens 101A and a plano-concave lens 102B, and the mirror 22 is formed in a curved shape and the PBS 21 in a planar shape. That is, the mirror 22 is given power during reflection. [Examples]

[0092] Figure 13 shows the configuration of the optical system 1 of the display device in Example 7. Examples 1 to 5 described the case in which the lens section 100 is constructed by joining a plano-concave lens 101 and a plano-convex lens 102. In contrast, in this example, the lens section 100B is constructed by joining a concave lens 101B with curved surfaces on both sides and a convex lens 102B with curved surfaces on both sides. The concave lens 101B and the convex lens 102B do not necessarily have to be joined.

[0093] Furthermore, in cases where the optical system 1 has multiple curved surfaces or where there is a difference in refractive index among the multiple lenses constituting the lens section, it is preferable that the reflective surface A, which is responsible for the main light-gathering power among the first and second transmitted reflective surfaces, satisfies the following condition of equation (6). When the power of reflection at reflective surface A is φA and the power of the entire optical system 1 is Φ, φA / Φ≧0.8 (6) By reducing the power of other curved surfaces to satisfy this condition, good imaging performance can be obtained in the optical system 1 that forms the imaging optical path and the imaging optical system 51 without complicating the configuration of the imaging optical system 51.

[0094] [Display device 1] Figure 14 shows a head-mounted display (HMD) as a specific example of the display devices of Examples 1 to 7. The HMD is mounted on the observer's head (in front of their eyes) by mounting gear (not shown).

[0095] The HMD includes image display elements RID and LID for the right and left eyes, a right-eye display optical system ROS that directs the display light from the right-eye image display element RID to the observer's right eye, and a left-eye display optical system LOS that directs the display light from the left-eye image display element LID to the observer's left eye.

[0096] By using optical system 1 described in Examples 1 to 7 as the right eye and left eye display optical systems ROS and LOS, a compact HMD can be realized.

[0097] [Display device 2] Figure 15 shows the configuration of an imaging device (hereinafter simply referred to as "camera") 200, such as a digital camera or video camera equipped with an electronic viewfinder (EVF), as a specific example of the display device of Examples 1 to 7.

[0098] The camera 200 includes an imaging optical system 201, an image sensor 202 such as a CCD sensor or CMOS sensor that captures (photoelectrically converts) an unshown subject through the imaging optical system 201, and an image processing unit 203 that generates image data using the signal output from the image sensor 202.

[0099] Image data generated by the image processing unit 203 is output to the display element 210 of the electronic viewfinder (EVF). The display element 210 displays the subject image corresponding to the image data on its display surface IP.

[0100] The electronic viewfinder (EVF) is equipped with an eyepiece optical system 211, which is composed of the optical system 1 described in Examples 1 to 7. The user (observer) of the camera 200 can magnify and observe the subject image displayed on the display element 210 through the eyepiece optical system 211.

[0101] By using optical system 1 of Examples 1 to 7 as the eyepiece optical system 211, a good subject image can be observed with a small electronic viewfinder.

[0102] The above embodiments include the following configuration.

[0103] (Composition 1) An optical system that guides the first wavelength light from the display element to the observation side, A first transmission and reflection surface that transmits first linearly polarized light and reflects second linearly polarized light having a different polarization direction from the first linearly polarized light, A second transmission-reflective surface is positioned on the observation side of the first transmission-reflective surface, and transmits a portion of the incident light and reflects the other portion regardless of the polarization direction of the light, The device includes an absorbing polarizer positioned on the observation side of the second transmission / reflection surface, which transmits third linearly polarized light and absorbs fourth linearly polarized light having a different polarization direction from the third linearly polarized light, At least a portion of the optical system guides a second wavelength light, which has a different wavelength range from the first wavelength light, incident from the observation side, to the imaging system. The transmittances of the first transmissive reflective surface for the first linearly polarized and second linearly polarized light of the first wavelength are Tp11 and Ts11, respectively, and the transmittances of the first transmissive reflective surface for the first linearly polarized and second linearly polarized light of the second wavelength are Tp12 and Ts12, respectively. When the transmittances of the absorbing polarizer for the third linearly polarized and fourth linearly polarized light of the first wavelength are Tp21 and Ts21, respectively, and the transmittances of the absorbing polarizer for the third linearly polarized and fourth linearly polarized light of the second wavelength are Tp22 and Ts22, respectively, Ts11 / Tp11≦0.1 Ts21 / Tp21 ≤ 0.1 Both conditions must be satisfied, and Ts12 / Tp12≧0.5 Ts22 / Tp22≧0.5 An optical system characterized by satisfying at least one of the following conditions. (Configuration 2) The first wavelength light is light in the visible wavelength range, The optical system according to configuration 1, characterized in that the second wavelength light is light in the infrared wavelength range. (Composition 3) The optical system according to configuration 1, characterized in that the first wavelength light from the display element is transmitted through the first transmission reflective surface, reflected by the second transmission reflective surface, reflected again by the first transmission reflective surface, transmitted through the second transmission reflective surface, and guided to the observation side by the absorbing polarizer. (Composition 4) When the second wavelength light from the light source is irradiated onto the observation side without passing through the optical system, and is reflected on the observation side and incident on the optical system, Ts12 / Tp12<0.5 Ts22 / Tp22≧0.5 An optical system of configuration 1 or 2 characterized by satisfying the following conditions. (Composition 5) When the aforementioned two-wavelength light from a light source is irradiated onto the observation side through at least a part of the optical system, reflected on the observation side, and incident back into the optical system, Ts12 / Tp12≧0.5 Ts22 / Tp22<0.5 An optical system of configuration 1 or 2 characterized by satisfying the following conditions. (Composition 6) When the aforementioned two-wavelength light from a light source is irradiated onto the observation side through at least a part of the optical system, reflected on the observation side, and incident back into the optical system, Ts12 / Tp12≧0.5 Ts22 / Tp22≧0.5 An optical system of configuration 1 or 2 characterized by satisfying the following conditions. (Composition 7) The optical system according to any one of configurations 1 to 6, characterized in that it has an absorbing polarizer other than the absorbing polarizer between the first transmissive reflective surface and the display element. (Composition 8) The optical system according to configuration 7, characterized in that it has a λ / 4 phase element between the other absorbing polarizer and the display element. (Composition 9) One of the first and second transmissive reflective surfaces acts as a reflective surface that has power, When the focal length of the reflective surface at the time of reflection is fA, and the air-equivalent optical path length of the first wavelength light from the reflection at the reflective surface to the pupil plane of the optical system on the observation side is LaA, 1.0 <LaA / fA≦2.5 An optical system according to any one of configurations 1 to 8, characterized by satisfying the following conditions. (Composition 10) The optical system described in any one of configurations 1 to 9, The aforementioned display button, The aforementioned imaging system, A display device characterized by having a light source that emits the second wavelength light irradiated onto the observation side.

[0104] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of Symbols]

[0105] 1 Optical system 20 Polarization Elements 11 Linear polarizer 21 PBS 22 Half Mirror 4 Display elements 5. Imaging Unit 6 Infrared light source

Claims

1. An optical system that guides the first wavelength light from the display element to the observation side, A first transmission and reflection surface that transmits first linearly polarized light and reflects second linearly polarized light having a different polarization direction from the first linearly polarized light, A second transmission-reflective surface is positioned on the observation side of the first transmission-reflective surface, and transmits a portion of the incident light and reflects the other portion regardless of the polarization direction of the light, The device includes an absorbing polarizer positioned on the observation side of the second transmission / reflection surface, which transmits third linearly polarized light and absorbs fourth linearly polarized light having a different polarization direction from the third linearly polarized light, At least a portion of the optical system guides a second wavelength light, which has a different wavelength range from the first wavelength light, incident from the observation side, to the imaging system. The transmittances of the first transmissive reflective surface for the first linearly polarized and second linearly polarized light of the first wavelength are Tp11 and Ts11, respectively, and the transmittances of the first transmissive reflective surface for the first linearly polarized and second linearly polarized light of the second wavelength are Tp12 and Ts12, respectively. When the transmittances of the absorbing polarizer for the third linearly polarized and fourth linearly polarized light of the first wavelength are Tp21 and Ts21, respectively, and the transmittances of the absorbing polarizer for the third linearly polarized and fourth linearly polarized light of the second wavelength are Tp22 and Ts22, respectively, Ts11 / Tp11≦0.1 Ts21 / Tp21≦0.1 Both conditions must be satisfied, and Ts12 / Tp12≧0.5 Ts22 / Tp22≧0.5 An optical system characterized by satisfying at least one of the following conditions.

2. The first wavelength light is light in the visible wavelength range, The optical system according to claim 1, characterized in that the second wavelength light is light in the infrared wavelength range.

3. The optical system according to claim 1, characterized in that the first wavelength light from the display element is transmitted through the first transmission reflective surface, reflected by the second transmission reflective surface, reflected again by the first transmission reflective surface, transmitted through the second transmission reflective surface, and guided to the observation side by the absorbing polarizer.

4. When the second wavelength light from the light source is irradiated onto the observation side without passing through the optical system, and is reflected on the observation side and incident on the optical system, Ts12 / Tp12<0.5 Ts22 / Tp22≧0.5 The optical system of the first type, characterized by satisfying the following conditions.

5. When the two wavelengths of light from the light source are irradiated onto the observation side through at least a part of the optical system, reflected on the observation side, and incident back into the optical system, Ts12 / Tp12≧0.5 Ts22 / Tp22<0.5 The optical system of the first type, characterized by satisfying the following conditions.

6. When the two wavelengths of light from the light source are irradiated onto the observation side through at least a part of the optical system, reflected on the observation side, and incident back into the optical system, Ts12 / Tp12≧0.5 Ts22 / Tp22≧0.5 The optical system of the first type, characterized by satisfying the following conditions.

7. The optical system according to claim 1, characterized in that it has an absorbing polarizer other than the absorbing polarizer between the first transmissive reflective surface and the display element.

8. The optical system according to claim 7, characterized in that it has a λ / 4 phase element between the other absorbing polarizer and the display element.

9. One of the first and second transmissive reflective surfaces acts as a reflective surface that has power, When the focal length of the reflective surface at the time of reflection is fA, and the air-equivalent optical path length of the first wavelength light from the reflection at the reflective surface to the pupil surface of the optical system on the observation side is LaA, 1.0<LaA / fA≦2.5 The optical system according to claim 1, characterized in that it satisfies the following conditions.

10. An optical system according to any one of claims 1 to 9, The aforementioned display button, The aforementioned imaging system, A display device characterized by having a light source that emits the second wavelength light irradiated onto the observation side.

Images