WO2025239164A1 - Head-mounted display - Google Patents

Abstract

The present invention addresses the problem of providing a head-mounted display having high sensing accuracy while having a function as a pancake lens optical system. The problem is solved by having a near-infrared light emission mechanism and a pancake lens optical system including a display, a half mirror, and a reflective polarizer, wherein: the near-infrared light emission mechanism is disposed on the display side with respect to the half mirror; the near-infrared light emission mechanism irradiates the reflective polarizer with near-infrared light having a wavelength λ1; the reflective polarizer has a reflection band in a wavelength region including visible light and the wavelength λ1; and the polarization state of visible light emitted from the display and incident first on the reflective polarizer, and the polarization state of near-infrared light emitted from the near-infrared light emission mechanism and incident first on the reflective polarizer are orthogonal to each other.

Description

head-mounted display

The present invention relates to a head-mounted display.

To experience so-called immersive virtual reality (VR), which blocks out external light from the real world, optical devices worn on a user's head and direct images to the user's eyes have been put to practical use. Such optical devices are generally called head-mounted displays.
As described above, a head-mounted display is worn on the user's head, and therefore, the head-mounted display is required to be small and thin.

For example, Patent Document 1 discloses a method for reducing the size and/or thickness of a display unit in a head-mounted display, which includes a display, a half mirror, and a reflective polarizer, and in which light emitted from the display (display image) is reflected between the reflective polarizer and the half mirror to travel back and forth, and then transmitted through the reflective polarizer to generate a virtual image.
Such an optical system is generally called a pancake lens optical system.

Reflective polarizers used in pancake lens optics generally exhibit a short-wavelength shift in the reflection band at high polar angles, which can cause color shifts when displaying at wide viewing angles. For this reason, reflective polarizers are designed to have a reflection band over a wide wavelength range.

Furthermore, in a pancake lens optical system, in order to increase the degree of freedom in lens design, it is desirable for one of the surfaces of the optical components that make up the pancake lens to have a curved shape with a high curvature.

When a reflective polarizer is molded to have a high curvature, some parts may be stretched at a high ratio and some parts at a low ratio, depending on how the reflective polarizer is molded.
In order to reflect light in the visible light range over the entire lens surface, it is necessary to provide a reflection band extending into the near-infrared range in addition to the visible range, taking into consideration the short-wave shift of the reflection band that occurs with stretching.

A known example of a reflective polarizer in which transmitted and reflected light are linearly polarized is the reflective linear polarizer described in Patent Document 2, which is made up of multiple alternating layers of two or more different types of birefringent layers.

A known example of a reflective polarizer in which transmitted and reflected light are circularly polarized is a film having a layer in which a cholesteric liquid crystal phase is fixed, as described in Patent Document 3. Furthermore, a film in which a quarter-phase retardation layer is laminated to the above-mentioned reflective linear polarizer can be used as a reflective polarizer in which reflected light is circularly polarized.

Patent No. 6501877 JP 2011-053705 A Patent No. 6277088

Here, the head mounted display may incorporate sensing means (detection means) that uses near-infrared light in order to perform eye tracking, iris authentication, face authentication, and the like.
For example, in the case of eye tracking, near-infrared light is emitted from a light source, which enters the user's eye, and the near-infrared light reflected by the user's eye is detected to detect the user's line of sight.

However, as mentioned above, if the reflection band of a reflective polarizer is designed to be wide and extends to the near-infrared region, it will also reflect near-infrared light used in sensing such as eye tracking, iris recognition, and face recognition. As a result, there are problems such as a decrease in the amount of near-infrared light that reaches the user's eye and/or the near-infrared light reflected by the reflective polarizer turning into noise, resulting in a decrease in sensing accuracy.
Therefore, an object of the present invention is to provide a head-mounted display that functions as a pancake lens optical system and also has high-precision sensing using near-infrared light.

The inventors conducted extensive research to solve the above problems, and as a result, completed the present invention. Specifically, they discovered that the above problems can be solved by the following configuration.

[1] A pancake lens optical system having, in this order, a display that emits at least visible light, a half mirror, and a reflective polarizer;
a near-infrared light emitting mechanism,
the near-infrared light emitting mechanism is disposed on the display side of the half mirror, and irradiates near-infrared light having a wavelength λ1 toward the reflective polarizer;
The reflective polarizer has a reflection band at least in part in a wavelength range that includes visible light and the wavelength λ1,
the polarization state of the visible light emitted from the display and first incident on the reflective polarizer and the polarization state of the near-infrared light emitted from the near-infrared light emitting mechanism and first incident on the reflective polarizer are orthogonal to each other;
Head-mounted display.
[2] The head-mounted display according to [1], wherein the reflective polarizer has a curved shape.
[3] A first linear polarizer is provided between the display and the half mirror,
The head-mounted display according to [1] or [2], further comprising an optical functional layer between the first linear polarizing plate and the reflective polarizer, the optical functional layer having a phase difference of 1/2 wavelength for near-infrared light of wavelength λ1 and no phase difference for visible light.
[4] The head mounted display according to [3], wherein the optical functional layer includes at least a layer formed by curing a rod-shaped liquid crystal compound and a layer formed by curing a discotic liquid crystal compound.
[5] A first linear polarizer is provided between the display and the half mirror,
A head-mounted display according to any one of [1] to [4], which has a linear polarizing plate between the first linear polarizing plate and the reflective polarizer, the linear polarizing plate having a polarization degree for near-infrared light of wavelength λ1 and no polarization degree for visible light.
[6] A first λ/4 phase plate is provided between the display and the half mirror,
a second λ/4 phase difference plate is provided on the viewing side of the half mirror;
The head-mounted display according to any one of [1] to [5], further comprising a near-infrared reflective polarizer between the first λ/4 retardation plate and the second λ/4 retardation plate, which reflects one circularly polarized light of wavelength λ1 and transmits the other circularly polarized light.

The present invention provides a head-mounted display that functions as a pancake lens optical system while also providing highly accurate sensing using near-infrared light.

FIG. 1 is a diagram conceptually illustrating an example of a head-mounted display according to the present invention. FIG. 2 is a conceptual diagram showing another example of the head-mounted display of the present invention. FIG. 3 is a conceptual diagram showing another example of the head-mounted display of the present invention. FIG. 4 is a conceptual diagram showing another example of the head-mounted display of the present invention. FIG. 5 is a conceptual diagram showing another example of the head-mounted display of the present invention. FIG. 6 is a diagram conceptually showing another example of the head-mounted display of the present invention. FIG. 7 is a conceptual diagram showing another example of the head-mounted display of the present invention. FIG. 8 is a diagram conceptually showing another example of the head-mounted display of the present invention. FIG. 9 is a conceptual diagram showing another example of the head-mounted display of the present invention.

The present invention will be described in detail below.
The following description of the components may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.

In this specification, "visible light" refers to light (electromagnetic waves) with a wavelength of 400 to 700 nm. Furthermore, "near-infrared light" refers to light with a wavelength of 800 to 2500 nm. When used for eye tracking and iris authentication, light with a wavelength of 800 to 1000 nm is preferred, and light with a wavelength of 800 to 900 nm is more preferred.
The wavelength of light can be measured using, for example, a spectrophotometer UV-3600 manufactured by Shimadzu Corporation.

In this specification, "having no phase difference with respect to visible light" means that the phase difference is 15 nm or less in the above-mentioned range of visible light, preferably 10 nm or less in the range of visible light, and more preferably 5 nm or less in the range of visible light.
In this specification, "having no polarization degree for visible light" means that the polarization degree within the range of visible light is 40% or less, preferably 20% or less, and more preferably 10% or less.

In this specification, "orthogonal" does not mean an angle of exactly 90°, but means 90°±10°, preferably 90°±5°. "Parallel" does not mean an angle of exactly 0°, but means 0°±10°, preferably 0°±5°. "45°" does not mean an angle of exactly 45°, but means 45°±10°, preferably 45°±5°.
It should be noted that the terms "orthogonal,""parallel," and "45°" used here refer to geometric angles such as the angle formed by two axes, and are different from the orthogonal polarization state of light described below.

In this specification, "absorption axis" refers to the polarization direction in which absorbance is maximized in a plane when linearly polarized light is incident. Furthermore, "reflection axis" refers to the polarization direction in which reflectance is maximized in a plane when linearly polarized light is incident. Furthermore, "transmission axis" refers to the direction in a plane that is perpendicular to the absorption axis or reflection axis. Furthermore, "slow axis" refers to the direction in a plane where the refractive index is maximized. Furthermore, "fast axis" refers to the direction in a plane where the refractive index is minimized, and is the direction perpendicular to the slow axis.

In this specification, unless otherwise specified, the phase difference means in-plane retardation and is expressed as Re(λ), where Re(λ) represents the in-plane retardation at a wavelength λ, and unless otherwise specified, the wavelength λ is 550 nm.
Furthermore, the retardation in the thickness direction at a wavelength λ is referred to as Rth(λ) in this specification. Unless otherwise specified, the wavelength λ is 550 nm.

Re(λ) and Rth(λ) can be values measured at a wavelength λ using an AxoScan OPMF-1 (manufactured by Optoscience). By inputting the average refractive index ((nx+ny+nz)/3) and film thickness (d (μm)) into AxoScan,
Slow axis direction (°)
Re(λ)=R0(λ)
Rth(λ)=((nx+ny)/2−nz)×d is calculated.
The degree of polarization of a linear polarizing plate can be measured using, for example, a polarizing film measuring device VAP-7070 manufactured by JASCO Corporation. The degree of polarization in the near-infrared wavelength range can also be calculated by overlaying a wire grid polarizing plate or the like with a known degree of polarization on a light source that emits infrared light to linearly polarize the emitted light, and then overlaying the linear polarizing plate to be measured, and measuring the transmittance of each of the transmission axis and absorption axis using a spectrophotometer or the like.

In addition, in this specification, the terms "liquid crystal composition" and "liquid crystal compound" also conceptually include those that no longer exhibit liquid crystallinity due to curing or other reasons.

The head-mounted display of the present invention will be described in detail below.
The head-mounted display of the present invention includes a display that emits at least visible light, a pancake lens optical system that includes a half mirror and a reflective polarizer in this order, and a near-infrared light emitting mechanism.
The near-infrared light emitting mechanism is disposed on the display side of the half mirror and irradiates near-infrared light of wavelength λ1 toward the reflective polarizer, which has a reflection band (reflection wavelength band) at least partially in a wavelength range that includes visible light and wavelength λ1.
In the head-mounted display of the present invention, the polarization state of the visible light emitted from the display and first incident on the reflective polarizer and the polarization state of the near-infrared light emitted from the near-infrared light emitting mechanism and first incident on the reflective polarizer are orthogonal to each other.
In addition to the components described above, the pancake lens optical system may further include other components that are included in known pancake lens optical systems, such as a λ/4 retardation plate and a linear polarizer, which will be described later.
In the head-mounted display of the present invention, the polarization state of visible light emitted from the display and first incident on the reflective polarizer is orthogonal to the polarization state of near-infrared light emitted from the near-infrared light emitting mechanism and first incident on the reflective polarizer. By having such a configuration, the head-mounted display of the present invention can function as a pancake lens optical system while also improving the accuracy of sensing, such as eye tracking, that uses near-infrared light. Specific embodiments include the first to third embodiments described below, but the present invention is not limited thereto.
Hereinafter, the head mounted displays of the first to third embodiments will be described.

[First embodiment of head-mounted display]
As described above, the head-mounted display of the present invention includes a display, a pancake lens optical system having a half mirror and a reflective polarizer, and a near-infrared light emitting mechanism.
In addition to these components, the head-mounted display of the first embodiment of the present invention has a first linear polarizer between the display and the half mirror, and further has an optical function layer between the first linear polarizer and the reflective polarizer. In the present invention, the optical function layer is an optical element that has a phase difference of ½ wavelength with respect to near-infrared light having a wavelength λ1 and has no phase difference with respect to visible light.
A first embodiment of the head-mounted display includes a display that emits at least visible light, a pancake lens optical system having a half mirror and a reflective polarizer in this order, a near-infrared light emitting mechanism, a first linear polarizer between the display and the half mirror, and an optical functional layer between the first linear polarizer and the reflective polarizer. In the first embodiment of the head-mounted display, the near-infrared light emitting mechanism is disposed on the display side of the half mirror and irradiates near-infrared light of wavelength λ1 toward the reflective polarizer, and the reflective polarizer has a reflection band in a wavelength range that includes at least a portion of visible light and the wavelength λ1. Furthermore, the first embodiment of the head-mounted display is a head-mounted display in which the polarization state of the visible light emitted from the display and initially incident on the reflective polarizer is orthogonal to the polarization state of the near-infrared light emitted from the near-infrared light emitting mechanism and initially incident on the reflective polarizer.

The head mounted display of the first embodiment will be specifically described below with reference to FIG.
Fig. 1 is a conceptual diagram illustrating an example of a head-mounted display according to a first embodiment of the present invention. A head-mounted display 1A shown in Fig. 1 uses a linearly polarized reflective polarizer as a reflective polarizer.
The head-mounted display 1A in Fig. 1 includes a near-infrared light emitting mechanism 5, a display 2, a first linear polarizer 8, an optical function layer 11, an optional first λ/4 retardation plate 6, a half mirror 3, an optional second λ/4 retardation plate 7, a linearly polarized reflective polarizer 4, and an optional second linear polarizer 9. In this embodiment, the position of the optical function layer 11 is not limited to the position shown in the illustration, and various positions can be used as long as it is between the first linear polarizer 8 and the linearly polarized reflective polarizer 4 (reflective polarizer). In this respect, the same applies to the embodiments shown in Figs. 2 and 3.
Although not shown, the head mounted display 1A in Fig. 1 preferably has a sensor for receiving and measuring near infrared light of wavelength λ1 emitted by the near infrared light emitting mechanism 5 and reflected by the user's eye. This also applies to the head mounted displays shown in Figs. 2 to 9 described below.

The head mounted display 1A shown in FIG. 1 preferably has lenses indicated by diagonal lines in the drawing.
1, in a preferred embodiment, the half mirror 3 and the second λ/4 retardation plate 7 are formed on the lens. Furthermore, in a preferred embodiment, the linearly polarized reflective polarizer 4 and the second linear polarizing plate 9 are also formed into a curved shape in accordance with the curved surface of the lens.
The present invention is not limited to this, and one or more of the half mirror 3, the second λ/4 retardation plate 7, the linearly polarized reflective polarizer 4, and the second linear polarizer 9 may be flat. However, considering the image quality of the virtual reality image, the aberration correction of the virtual reality image, and the miniaturization and weight reduction of the pancake lens, it is preferable that the half mirror 3 and the components downstream of the half mirror 3, i.e., the components constituting the so-called pancake lens, be formed into a curved shape according to the shape of the lens. Note that "downstream" refers to the downstream direction from the display 2 toward the user.
The same applies to the head-mounted displays shown in FIGS. 2 to 9 in this respect.

In the present invention, there is no limitation on the lens, and various lenses used in so-called pancake lenses can be used.
Examples of lenses include convex lenses and concave lenses.
Examples of the convex lens that can be used include a biconvex lens, a plano-convex lens, and a convex meniscus lens. Examples of the concave lens that can be used include a biconcave lens, a plano-concave lens, and a concave meniscus lens.
As the lens, a convex meniscus lens or a concave meniscus lens is preferable in order to widen the angle of view, and a concave meniscus lens is more preferable in terms of minimizing chromatic aberration.
Lens materials that are transparent to visible light, such as glass, crystal, plastic, etc. Lens birefringence can cause rainbow irregularities and light leakage, so the smaller the birefringence, the better, and materials with substantially zero birefringence are more preferable.
The lenses constituting the head mounted display of the present invention may be flat lenses, such as volume holograms and liquid crystal diffraction elements.

The operation of the head mounted display 1A of FIG. 1 will be described.
In FIG. 1, visible light emitted from the display 2 , that is, a visible light image displayed by the display 2 , first enters a first linear polarizer 8 .
The visible light passes through the first linear polarizer 8 to become linearly polarized light, and enters the optical function layer 11. In this example, as an example, the light transmitted through the linear polarizer 8 becomes linearly polarized light in the up and down direction in the figure.
As described above, the optical function layer 11 is an optical element that has a phase difference of 1/2 wavelength with respect to near-infrared light with wavelength λ1, but has no phase difference with respect to visible light. Therefore, even when the visible light emitted from the display 2 passes through the optical function layer 11, the polarization does not change and the visible light remains linearly polarized in the up and down direction in the figure.
The visible light, which is linearly polarized light in the vertical direction in the figure, then becomes circularly polarized light by passing through the first λ/4 retardation plate 6. In this example, as an example, the first λ/4 retardation plate 6 converts the linearly polarized light in the vertical direction in the figure into right-handed circularly polarized light.

The right-handed circularly polarized visible light passes through the half mirror 3 and the lens, and then passes through the second λ/4 retardation plate 7 to become linearly polarized light. In this example, as an example, the second λ/4 retardation plate 7 converts the right-handed circularly polarized light into linearly polarized light in the up-down direction in the figure.
The visible light, which is linearly polarized in the vertical direction in the figure, then enters the linearly polarized reflective polarizer 4 (initial incidence).
In this example, the linearly polarized reflective polarizer 4 is, for example, a reflective polarizer that reflects linearly polarized light in the vertical direction in the figure and transmits linearly polarized light perpendicular to the plane of the paper. Therefore, visible light that is linearly polarized in the vertical direction in the figure and that is incident on the linearly polarized reflective polarizer 4 is reflected by the linearly polarized reflective polarizer 4.

The visible light that is linearly polarized in the vertical direction in the figure and that is reflected by the linearly polarized reflective polarizer 4 is again incident on and transmitted through the second λ/4 retardation plate 7. As described above, the second λ/4 retardation plate 7 converts right-handed circularly polarized light that is linearly polarized in the vertical direction in the figure into right-handed circularly polarized light. Therefore, the visible light that is linearly polarized in the vertical direction in the figure and that is incident on the second λ/4 retardation plate 7 is converted into right-handed circularly polarized light.
The right-handed circularly polarized visible light converted by the second λ/4 phase difference plate 7 passes through the lens and enters the half mirror 3, where half of it is reflected. During this reflection, the right-handed circularly polarized visible light becomes circularly polarized light in a direction different from the original circular polarization, i.e., left-handed circularly polarized light in this example.
The left-handed circularly polarized visible light reflected by the half mirror 3 is again incident on the second λ/4 retardation plate 7. As described above, the second λ/4 retardation plate 7 converts right-handed circularly polarized light, which is linearly polarized light in the up-down direction in the figure, into right-handed circularly polarized light. Therefore, the left-handed circularly polarized visible light incident on the second λ/4 retardation plate 7 is converted into linearly polarized light in the direction perpendicular to the plane of the drawing.
The visible light, which is linearly polarized in a direction perpendicular to the plane of the paper, then enters the linearly polarized reflective polarizer 4. As described above, the linearly polarized reflective polarizer 4 is a linearly polarized reflective polarizer that reflects linearly polarized light in the up-down direction in the figure and transmits linearly polarized light perpendicular to the plane of the paper. Therefore, the visible light, which is linearly polarized in a direction perpendicular to the plane of the paper, transmits through the linearly polarized reflective polarizer 4.
The visible light, which is linearly polarized in a direction perpendicular to the paper surface and transmitted through the linearly polarized reflective polarizer 4, is transmitted through the second linear polarizer 9, which transmits light linearly polarized in this direction, and is then viewed by the user. As a result, the image displayed on the display is observed by the user.

1, near-infrared light having a wavelength λ1 emitted from the near-infrared light emitting mechanism 5 passes through the display 2 and similarly enters the first linear polarizer 8. In the following description, the "near-infrared light having a wavelength λ1" will also be simply referred to as "near-infrared light."
That is, in this example, near-infrared light is transmissive (can pass through) through the display 2. This also applies to other head-mounted displays in which the near-infrared light emitting mechanism 5 is disposed on the back side of the display 2 relative to the user.
Like the visible light emitted from the display 2, the near-infrared light emitted from the near-infrared light emitting mechanism 5 also passes through the linear polarizer 8 and becomes linearly polarized light in the up and down directions in the figure.
Similarly, near-infrared light that is linearly polarized in the vertical direction in the figure is incident on the optical function layer 11. As described above, the optical function layer 11 is an optical element that has a phase difference of ½ wavelength with respect to near-infrared light with wavelength λ1 and has no phase difference with respect to visible light. Therefore, the near-infrared light emitted by the near-infrared light emitting mechanism 5 is converted by the optical function layer 11 into light that is linearly polarized in the direction perpendicular to the plane of the drawing.
The near-infrared light, which is linearly polarized in a direction perpendicular to the paper surface, then passes through the first λ/4 retardation plate 6 and becomes circularly polarized. As described above, the first λ/4 retardation plate 6 converts linearly polarized light in the up-down direction in the drawing into right-handed circularly polarized light. Therefore, the near-infrared light, which is linearly polarized in a direction perpendicular to the paper surface, is converted into left-handed circularly polarized light by the first λ/4 retardation plate 6.

The left-handed circularly polarized near-infrared light passes through the half mirror 3 and the lens, and then passes through the second λ/4 retardation plate 7 to become linearly polarized light. As described above, the second λ/4 retardation plate 7 converts right-handed circularly polarized light into linearly polarized light in the up-down direction in the figure. Therefore, the left-handed circularly polarized near-infrared light passes through the second λ/4 retardation plate 7 and is converted into linearly polarized light in the direction perpendicular to the plane of the drawing.
The near-infrared light, which is linearly polarized in a direction perpendicular to the paper surface, then enters the linearly polarized reflective polarizer 4 (initial incidence).
Here, as described above, the visible light emitted from the display 2 is linearly polarized in the up-down direction in the drawing when it first enters the linearly polarized reflective polarizer 4. That is, in the head-mounted display 1A, the polarization state of the visible light that first enters the linearly polarized reflective polarizer 4 and the polarization state of the near-infrared light that first enters the linearly polarized reflective polarizer 4 are orthogonal to each other.
As described above, the linearly polarized reflective polarizer 4 is a linearly polarized reflective polarizer that reflects light linearly polarized in the vertical direction in the figure and transmits light linearly polarized in the direction perpendicular to the plane of the paper. Therefore, near-infrared light that is linearly polarized in the direction perpendicular to the plane of the paper and that is incident on the linearly polarized reflective polarizer 4 is transmitted through the linearly polarized reflective polarizer 4.

The near-infrared light that is linearly polarized in a direction perpendicular to the paper surface and that passes through the linearly polarized reflective polarizer 4 passes through the second linear polarizer 9 that transmits linearly polarized light in this direction, enters the user's eyes, and is reflected, for example, in a direction that corresponds to the user's line of sight.
Near-infrared light reflected by the user's eyes is incident on a sensor (not shown) and is photometrically measured, for example, for eye tracking.

As described above, in the head-mounted display of the present invention, the polarization state of the visible light that first enters the reflective polarizer and the polarization state of the infrared light that first enters the reflective polarizer are orthogonal to each other.
Therefore, for example, even a reflective polarizer having a reflection band in a wavelength range including visible light and near-infrared light, in which the reflection band is expanded to the near-infrared light range in order to accommodate a short-wave shift in the reflection wavelength range resulting from molding into a curved surface shape according to the lens, can transmit near-infrared light for sensing without reflecting it. This effect can also be suitably obtained when the reflective polarizer is molded with a high curvature in accordance with lenses with increased design freedom for purposes such as correcting lens aberrations and expanding the FOV (Field of View).
Therefore, visible light is magnified by the pancake lens optical system and becomes visible to the user, but near-infrared light passes through the pancake lens optical system and can be used for sensing such as eye tracking and iris authentication.
Furthermore, according to the present invention, near-infrared light used for sensing is not unnecessarily reflected by the reflective polarizer, allowing a high amount of near-infrared light to be incident on the user's eyes. Furthermore, since the near-infrared light used for sensing is not unnecessarily reflected by the reflective polarizer, it is possible to prevent near-infrared light unnecessarily reflected by the reflective polarizer from becoming sensing noise. As a result, the head-mounted display of the present invention can perform sensing such as eye tracking using near-infrared light with high accuracy.

Fig. 2 is a conceptual diagram of another example of a head-mounted display, which is a modified example of the first embodiment. Note that the head-mounted displays shown in Figs. 2 to 9 below use multiple components that are the same as those in the head-mounted display shown in Fig. 1. Therefore, the same components are given the same reference numerals, and the following description will mainly focus on the different parts.
2 , the near-infrared light emitting mechanism 5 may be disposed on a side surface of the display 2. In this case, the head mounted display 1B also includes a first linear polarizer 8, an optical function layer 11 between the first linear polarizer 8 and the linearly polarized reflective polarizer 4, and a first λ/4 retardation plate 6, in correspondence with the display 2 and the near-infrared light emitting mechanism 5, as in the previous case.
When the near-infrared light emitting mechanism 5 is disposed on the side surface of the display 2, the optical function layer 11 may be formed only on the optical path of the near-infrared light emitted by the near-infrared light emitting mechanism 5. In other words, the optical function layer 11 may be formed by patterning on the optical path of the near-infrared light in another optical member.
The operation of the head mounted display 1B in FIG. 2 is similar to the operation of the head mounted display 1A in FIG.

Fig. 3 is a conceptual diagram showing another example of a head-mounted display, which is a modification of the first embodiment. The head-mounted display 1C in Fig. 3 uses a circularly polarized reflective polarizer as the reflective polarizer.
3 includes a near-infrared light emitting mechanism 5, a display 2, a first linear polarizing plate 8, an optical function layer 11, an optional first λ/4 retardation plate 6, a half mirror 3, a circularly polarized reflective polarizer 10, an optional second λ/4 retardation plate 7, and an optional second linear polarizing plate 9. As described above, the optical function layer 11 is an optical element that has a phase difference of ½ wavelength with respect to near-infrared light (near-infrared light having a wavelength λ1) and has no phase difference with respect to visible light.

The operation of the head mounted display 1C of FIG. 3 will be described.
In the head-mounted display 1C shown in Figure 3, as in the example shown in Figure 1, visible light emitted from the display 2 passes through the first linear polarizer 8 and becomes linearly polarized light in the up and down direction in the figure, passes through the optical function layer 11, which has no phase difference with respect to visible light, without changing its polarization state, and passes through the first λ/4 retardation plate 6 to be converted into right-handed circularly polarized light.
The right-handed circularly polarized visible light passes through the half mirror 3 and the lens, and then enters the circularly polarized reflective polarizer 10 (initial incidence). In this example, the circularly polarized reflective polarizer 10 is, for example, a reflective polarizer that reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the right-handed circularly polarized visible light is reflected by the circularly polarized reflective polarizer 10.
As before, the right-handed circularly polarized visible light reflected by the circularly polarized reflective polarizer 10 passes through the lens and enters the half mirror 3, where half of the light is reflected. Furthermore, during this reflection, the right-handed circularly polarized visible light becomes left-handed circularly polarized light.
The left-handed circularly polarized visible light reflected by the half mirror 3 is incident again on the circularly polarized reflective polarizer 10. As described above, the circularly polarized reflective polarizer 10 reflects right-handed circularly polarized light and transmits left-handed circularly polarized light, so the left-handed circularly polarized visible light is transmitted through the circularly polarized reflective polarizer 10.
The left-handed circularly polarized visible light transmitted through the circularly polarized light reflective polarizer 10 is incident on the second λ/4 retardation plate 7 and converted into linearly polarized light in the direction perpendicular to the paper surface.
The visible light converted into linearly polarized light perpendicular to the plane of the paper by the second λ/4 phase difference plate 7 passes through the second linear polarizer 9, which transmits linearly polarized light in this direction, and is visible to the user, as before.

On the other hand, in the head-mounted display 1C of Figure 3, the near-infrared light (near-infrared light with wavelength λ1) emitted from the near-infrared light emitting mechanism 5 passes through the first linear polarizer 8 and becomes linearly polarized light in the up and down direction in the figure, as in the example shown in Figure 1, and is converted into linearly polarized light in the direction perpendicular to the paper surface by the optical function layer 11 which has a phase difference of 1/2 wavelength with respect to the near-infrared light.
The near-infrared light, which is linearly polarized in a direction perpendicular to the paper surface, is then converted into left-handed circularly polarized light by the first λ/4 retardation plate 6 .
The left-handed circularly polarized near-infrared light passes through the half mirror 3 and the lens, and then enters the circularly polarized reflective polarizer 10 (initial incidence). As described above, the circularly polarized reflective polarizer 10 is a reflective polarizer that reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the left-handed circularly polarized near-infrared light passes through the circularly polarized reflective polarizer 10.
As described above, the visible light emitted from the display 2 is right-handed circularly polarized light when it first enters the circularly polarized reflective polarizer 10. That is, also in the head-mounted display 1C shown in Fig. 3 , the polarization state of the visible light that first enters the circularly polarized reflective polarizer 10 is orthogonal to the polarization state of the near-infrared light that first enters the circularly polarized reflective polarizer 10.

The left-handed circularly polarized near-infrared light transmitted through the circularly polarized light reflective polarizer 10 is incident on the second λ/4 retardation plate 7 and converted into linearly polarized light in the direction perpendicular to the paper surface.
The near-infrared light converted into linearly polarized light perpendicular to the paper surface by the second λ/4 phase difference plate 7 passes through the second linear polarizing plate 9 that transmits linearly polarized light in this direction, enters the user's eye, and is reflected, for example, in a direction corresponding to the user's line of sight.
Near-infrared light reflected by the user's eyes is incident on a sensor (not shown) and photometry is performed, for example, for eye tracking.

As described above, in this example as well, the polarization state of the visible light that first enters the reflective polarizer and the polarization state of the infrared light that first enters the reflective polarizer are orthogonal to each other.
Therefore, similar to the head-mounted display 1A shown in Figure 1, visible light is magnified by the pancake lens optical system and becomes visible to the user, but near-infrared light passes through, making it possible to perform highly accurate sensing such as eye tracking and iris authentication.
3, even in an embodiment in which a circularly polarized reflective polarizer is used as the reflective polarizer, the near-infrared light emitting mechanism 5 may be disposed on the side of the display 2, as in the head-mounted display 1B shown in Fig. 2. In this regard, the same applies to head-mounted displays in second and third embodiments described later that use a circularly polarized reflective polarizer as the reflective polarizer.

The members used in the first embodiment (FIGS. 1 to 3) will be described.
<Display>
The head-mounted display of the present invention has a display.
As the display, various known displays (image display elements) used in head-mounted displays can be used.
For example, the display may be a self-luminous display panel such as an LED (light emitting diode) array, an OLED (organic light emitting diode) display panel, a micro LED panel, or a mini LED panel. Also, a display combining a transmissive liquid crystal panel and a backlight unit may be used.

<Half mirror>
The head-mounted display of the present invention has a half mirror.
The half mirror is a conventionally known half mirror that transmits approximately half of the incident light and reflects the remaining half.
The transmittance of the half mirror is preferably 50±30%, more preferably 50±10%, and even more preferably 50%.
The half mirror has a structure in which a reflective layer made of a metal such as silver or aluminum is formed on a substrate made of, for example, a transparent resin such as polyethylene terephthalate (PET), cycloolefin polymer (COP), or polymethyl methacrylate (PMMA), or glass. The reflective layer made of a metal such as silver or aluminum is formed on the surface of the substrate by vapor deposition or the like. The thickness of the reflective layer is preferably 1 to 20 nm, more preferably 2 to 10 nm, and even more preferably 3 to 6 nm.

<<Reflective polarizer>>
The head-mounted display of the present invention has a reflective polarizer. The reflective polarizer is a polarizer that has the function of reflecting one polarized light of incident light and transmitting the other polarized light. The reflected light and the transmitted light by the reflective polarizer are polarized in mutually orthogonal directions.
Furthermore, as described above, in the head-mounted display of the present invention, the polarization state of visible light that is emitted from the display and first enters the reflective polarizer and the polarization state of near-infrared light (near-infrared light with wavelength λ1) that is emitted from the near-infrared light emitting mechanism and first enters the reflective polarizer are orthogonal to each other. As described above, the present invention has such a configuration, thereby realizing image display using visible light and high-precision sensing using near-infrared light.

Here, the orthogonal polarization states refer to polarization states located at antipodes on the Poincaré sphere, such as linearly polarized light that is orthogonal to each other. Generally, right-handed circularly polarized light (right-handed circularly polarized light) and left-handed circularly polarized light (left-handed circularly polarized light) are not referred to as orthogonal polarization states, but in the present invention, right-handed circularly polarized light and left-handed circularly polarized light are also interpreted as orthogonal polarization states.
However, in the present invention, the mutually orthogonal polarization states do not necessarily mean polarization states located at completely antipodal points on the Poincaré sphere, or completely right-handed circularly polarized light and completely left-handed circularly polarized light. In other words, in the present invention, the mutually orthogonal polarization states also include cases with unavoidable deviations from completely orthogonal, that is, unavoidable errors, such as slight positional deviations on the Poincaré sphere, slightly elliptical circularly polarized light, and a state in which one circularly polarized light is slightly mixed with the other circularly polarized light.

It is sufficient that at least a portion of the reflective polarizer has a reflection band in a wavelength range that includes visible light (visible light emitted by a display) and the wavelength λ1, and the entire surface of the reflective polarizer may have a reflection band in a wavelength range that includes visible light and the wavelength λ1. When the reflective polarizer has a reflection band in this range, it becomes possible to reliably reflect visible light of the target wavelength, i.e., the image displayed by the display, even when the reflective polarizer is molded into a curved shape with a high curvature in accordance with a lens.
The reflective polarizer includes a linearly polarized reflective polarizer and a circularly polarized reflective polarizer.
When the pancake lens includes a lens as in the illustrated example, the reflective polarizer preferably has a curved shape corresponding to the curved surface of the lens. The curvature of the reflective polarizer is preferably 10 to 150 mm, more preferably 30 to 120 mm.
The thickness of the reflective polarizer may be adjusted appropriately depending on the type of reflective polarizer, etc., to a thickness that can sufficiently reflect polarized light that should be reflected and can sufficiently transmit polarized light that should be transmitted.

<Linear polarized light reflective polarizer>
A linearly polarized reflective polarizer is a polarizer that transmits linearly polarized light in a certain direction and reflects linearly polarized light in a direction perpendicular to the linearly polarized light.
Examples of linearly polarized reflective polarizers include a film obtained by stretching a dielectric multilayer film, as described in JP 2011-053705 A, and a wire-grid polarizer, as described in JP 2015-028656 A. Commercially available linearly polarized reflective polarizers can also be suitably used. Examples of commercially available linearly polarized reflective polarizers include multilayer polymer reflective polarizers manufactured by 3M (product names APF, DBEF, IQPE, etc.) and wire-grid polarizers manufactured by AGC (product name WGF).

<Circularly polarized reflective polarizer>
A circularly polarized light reflective polarizer is a polarizer that transmits right-handed or left-handed circularly polarized light and reflects circularly polarized light that has the opposite rotation direction to the transmitted circularly polarized light.
An example of a circularly polarized reflective polarizer is a circularly polarized reflective polarizer having a cholesteric liquid crystal layer. The cholesteric liquid crystal layer is a liquid crystal layer formed by fixing a cholesterically oriented liquid crystal phase (cholesteric liquid crystal phase).
As is well known, a cholesteric liquid crystal layer has a helical structure in which liquid crystal compounds are spirally rotated and stacked, and the structure in which liquid crystal compounds are spirally rotated and stacked one turn (360° rotation) is defined as one helical pitch (helical pitch), and the helically rotated liquid crystal compounds have a structure in which multiple pitches are stacked.
A cholesteric liquid crystal layer reflects right-handed or left-handed circularly polarized light in a specific wavelength range and transmits other light, depending on the length of the helical pitch and the sense of rotation of the helix by the liquid crystal compound.
Therefore, when the head-mounted display displays color images, the circularly polarized reflective polarizer may have multiple cholesteric liquid crystal layers, such as a cholesteric liquid crystal layer having a central wavelength that selectively reflects red light, a cholesteric liquid crystal layer having a central wavelength that selectively reflects green light, and a cholesteric liquid crystal layer having a central wavelength that selectively reflects blue light.
The circularly polarized reflective polarizer may be made of, for example, a rod-shaped liquid crystal compound or a discotic liquid crystal compound that is cholesterically aligned.
Although the circularly polarized reflective polarizer and the linearly polarized reflective polarizer basically need only have a reflection band for the light (display image) emitted from the display, it is preferable that they have a reflection band up to the near-infrared light region, taking into consideration the wavelength shift caused by curved surface molding. More specifically, in the present invention, the reflective polarizer has a reflection band in a wavelength region including visible light and the wavelength λ1.

<λ/4 retardation plate>
The head mounted display of the present invention may have a λ/4 retardation plate (a first λ/4 retardation plate and/or a second λ/4 retardation plate).
The λ/4 retardation plate can be any retardation element that has a phase delay amount equivalent to a quarter wavelength in a predetermined wavelength range, and examples thereof include an inorganic retardation plate, a stretched polymer retardation plate, a liquid crystal retardation plate in which a liquid crystal compound or a polymerizable liquid crystal compound is fixed in an oriented state, and a metasurface retardation plate.
Here, having a phase delay amount equivalent to a quarter wavelength means that Re(550) is in the range of 120 nm to 160 nm.
When the λ/4 retardation plate is used for visible light, it preferably exhibits quarter-wave characteristics over a wide band, and its wavelength dispersion preferably exhibits the relationship Re(450)<Re(550)≦Re(650), i.e., so-called reverse wavelength dispersion.
The λ/4 retardation plate may be a single-layer film or sheet, or may be a laminate of a plurality of films or sheets that exhibits its properties.

<Linear polarizer>
The head mounted display of the present invention may have a linear polarizer (first linear polarizer and/or second linear polarizer).
Examples of linear polarizing plates that can be used include those in which iodine or a dichroic dye having absorption in the visible range is adsorbed and aligned on a polyvinyl alcohol-based resin film, those in which a dichroic dye having absorption in the visible range is dissolved or dispersed in a liquid crystal composition to form and fix an aligned state, and those in which a wire grid is applied.

<Near infrared light emission mechanism>
The head mounted display of the present invention has a near-infrared light emitting mechanism that is disposed on the display side of the half mirror and irradiates near-infrared light with a wavelength λ1 toward the reflective polarizer.
The wavelength λ1 may be in the near-infrared light range (800 to 2500 nm) described above, but as described above, it is preferably 800 to 1000 nm, and more preferably 800 to 900 nm.
The near-infrared light emitting mechanism may be any of various known mechanisms having a light source that irradiates near-infrared light.
Any known light source can be used as the light source emitting near-infrared light. Light sources are typically IR-emitting LED devices, IR lasers, and various lamps with an emission band in the near-infrared region. These light sources emit light with a certain range of wavelengths, but in the present invention, the wavelength λ1 is the central wavelength (peak wavelength) of the light emitted by the light source.
Furthermore, the near-infrared light emitting mechanism may have, in addition to the light source, various optical members that known light emitting mechanisms have, such as a lens, a collimator lens, a beam diameter adjusting means, and an optical path adjusting means such as a mirror.

<Optical functional layer>
The head mounted display of the present invention may have an optical function layer.
As described above, in the present invention, the optical functional layer is an optical element that has a phase difference of 1/2 wavelength with respect to near-infrared light (near-infrared light with a wavelength λ1) and has no phase difference with respect to visible light. That is, in the present invention, the optical functional layer is an optical element that acts as a λ/2 retardation plate with respect to light of a specific wavelength in the near-infrared range (near-infrared light with a wavelength λ1) and does not act as a retardation layer with respect to other light (visible light).
As an example of such an optical functional layer, a Solk filter is known, which is formed by alternately laminating birefringent plates (λ/2 retardation plates) having the same thickness and in which the angle between the direction of the transmission axis of the polarizer and the slow axis is +ρ and birefringent plates having an angle of −ρ, as described in patent documents such as JP 2004-101577 A. In this Solk filter, by defining λ as the wavelength λ1 of the near-infrared light emitting mechanism, a retardation plate having a wavelength of ½ of λ1 is obtained.
The λ/2 retarder may be a liquid crystal retarder in which a liquid crystal compound or a polymerizable liquid crystal compound is fixed in an aligned state, and it is preferable to use a liquid crystal retarder containing a rod-shaped liquid crystal compound and a discotic liquid crystal compound, because the retardation (Rth) in the thickness direction of the rod-shaped liquid crystal compound layer can be offset by the retardation in the thickness direction of the discotic liquid crystal compound layer, resulting in less wavelength shift when viewed from an oblique direction.

[Head-mounted display according to the second embodiment]
As described above, the head-mounted display of the present invention includes a display, a pancake lens optical system having a half mirror and a reflective polarizer, and a near-infrared light emitting mechanism.
In addition to these components, the head-mounted display of the second embodiment of the present invention has a first linear polarizing plate between the display and the half mirror, and further has a linear polarizing plate between the first linear polarizing plate and the reflective polarizer that has a polarization degree for near-infrared light of wavelength λ1 and no polarization degree for visible light.
A head-mounted display according to a second embodiment includes a pancake lens optical system having, in this order, a display that emits at least visible light, a half mirror, and a reflective polarizer, a near-infrared light emitting mechanism, a first linear polarizer disposed between the display and the half mirror, and a linear polarizer disposed between the first linear polarizer and the reflective polarizer, the linear polarizer having a polarization degree for near-infrared light of wavelength λ1 but not for visible light. In the following description, the linear polarizer having a polarization degree for near-infrared light of wavelength λ1 but not for visible light will also be simply referred to as a "near-infrared linear polarizer."
In the second embodiment of the present invention, the near-infrared light emitting mechanism is also disposed on the display side of the half mirror and irradiates near-infrared light of wavelength λ1 toward the reflective polarizer, and at least a portion of the reflective polarizer has a reflection band in a wavelength range that includes visible light and wavelength λ1. Furthermore, the head-mounted display of the second embodiment of the present invention is also a head-mounted display in which the polarization state of the visible light that is emitted from the display and first incident on the reflective polarizer and the polarization state of the near-infrared light that is emitted from the near-infrared light emitting mechanism and first incident on the reflective polarizer are orthogonal to each other.

The head mounted display of the second embodiment will be specifically described below with reference to FIG.
Fig. 4 is a conceptual diagram illustrating an example of a head-mounted display according to a second embodiment of the present invention. A head-mounted display 1D shown in Fig. 4 uses a linearly polarized reflective polarizer as a reflective polarizer.
4 includes a near-infrared light emitting mechanism 5, a display 2, a first linear polarizer 8, a near-infrared linear polarizer 12, an optional first λ/4 retardation plate 6, a half mirror 3, an optional second λ/4 retardation plate 7, a linearly polarized reflective polarizer 4, and an optional second linear polarizer 9. In this example, the first linear polarizer 5 is, as a preferred embodiment, a linear polarizer that has no polarization degree in the near-infrared light region or has a small polarization degree in the near-infrared light region, as will be described later.
The first linear polarizer 8 and the near-infrared linear polarizer 12 are arranged so that the angles formed by their respective absorption axes are perpendicular to each other.
Furthermore, in this embodiment, the position of the near-infrared linear polarizer 12 is not limited to the position shown in the illustration, and various positions can be used as long as it is between the first linear polarizer 8 and the linearly polarized reflective polarizer 4 (reflective polarizer). In this respect, the same applies to the embodiments shown in Figures 5 and 6 described below.

The operation of the head mounted display 1D of FIG. 4 will be described.
In the head-mounted display 1D shown in Figure 4, as in the first embodiment shown in Figure 1, visible light emitted from the display 2 passes through the first linear polarizer 8, becomes linearly polarized light in the vertical direction in the figure, and enters the near-infrared linear polarizer 12.
As described above, the near-infrared linear polarizer 12 is a linear polarizer that has a degree of polarization for near-infrared light of wavelength λ1 but has no degree of polarization for visible light. Therefore, visible light that is linearly polarized in the up and down direction in the figure passes through the near-infrared linear polarizer 12 without any change in polarization.
The visible light, which is linearly polarized in the vertical direction in the figure, then passes through the first λ/4 phase plate 6 and is converted into right-handed circularly polarized light, as before.
The right-handed circularly polarized visible light passes through the half mirror 3 and the lens, and then passes through the second λ/4 retardation plate 7, where it is converted into linearly polarized light in the vertical direction in the figure, as in the above example, and enters the linearly polarized reflective polarizer 4 (initial incidence). As described above, the linearly polarized reflective polarizer 4 is a reflective polarizer that reflects linearly polarized light in the vertical direction in the figure and transmits linearly polarized light perpendicular to the paper surface. Therefore, the visible light that is linearly polarized in the vertical direction in the figure is reflected by the linearly polarized reflective polarizer 4. The visible light that is linearly polarized in the vertical direction in the figure and reflected by the linearly polarized reflective polarizer 4 passes through the second λ/4 retardation plate 7 and is converted into right-handed circularly polarized light.
The right-handed circularly polarized visible light passes through the lens and is incident on the half mirror 3, where half of the light is reflected. The right-handed circularly polarized visible light is converted into left-handed circularly polarized light by this reflection.
The visible light that has been reflected by the half mirror 3 and turned into left-handed circularly polarized light is converted into linearly polarized light in a direction perpendicular to the plane of the paper by the second λ/4 retardation plate 7. The visible light that has been converted into linearly polarized light in a direction perpendicular to the plane of the paper passes through the linearly polarized reflective polarizer 4.
Visible light that is linearly polarized in a direction perpendicular to the paper surface and that has passed through the linearly polarized reflective polarizer 4 passes through the second linear polarizer 9 that transmits light that is linearly polarized in this direction, and is visible to the user.

4, the near-infrared light (near-infrared light with wavelength λ1) emitted from the near-infrared light emitting mechanism 5 is also incident on the first linear polarizer 8. In this example, the first linear polarizer 8 is preferably a linear polarizer that has no polarization degree in the near-infrared light region or has a small polarization degree in the near-infrared light region. Therefore, the polarization state of the near-infrared light that has passed through the first linear polarizer 8 is hardly changed.
The near-infrared light transmitted through the first linear polarizer 8 then enters the near-infrared linear polarizer 12. As described above, the near-infrared linear polarizer 12 is a linear polarizer that has a degree of polarization for near-infrared light with wavelength λ1 but has no degree of polarization for visible light. In this example, the near-infrared linear polarizer 12 has a transmission axis perpendicular to the paper surface. Therefore, the near-infrared light transmits through the near-infrared linear polarizer 12 and becomes linearly polarized light perpendicular to the paper surface.
The near-infrared light, which is linearly polarized in a direction perpendicular to the paper surface, then passes through the first λ/4 phase plate 6 and is converted into left-handed circularly polarized light.
The left-handed circularly polarized near-infrared light passes through the half mirror 3 and the lens, and then passes through the second λ/4 retardation plate 7. As in the above example, the light is converted into linearly polarized light perpendicular to the plane of the paper, and enters the linearly polarized reflective polarizer 4 (initial incidence). As described above, the linearly polarized reflective polarizer 4 is a reflective polarizer that reflects linearly polarized light in the up-down direction in the figure and transmits linearly polarized light perpendicular to the plane of the paper. Therefore, the near-infrared light that is linearly polarized perpendicular to the plane of the paper passes through the linearly polarized reflective polarizer 4.
Here, as described above, the visible light emitted from the display 2 is linearly polarized in the up-down direction in the drawing when it first enters the linearly polarized reflective polarizer 4. That is, also in the head-mounted display 1D shown in Fig. 4 , the polarization state of the visible light that first enters the linearly polarized reflective polarizer 4 and the polarization state of the near-infrared light that first enters the linearly polarized reflective polarizer 4 are orthogonal to each other.

The near-infrared light that is linearly polarized in a direction perpendicular to the paper surface and that passes through the linearly polarized reflective polarizer 4 passes through the second linear polarizer 9 that transmits linearly polarized light in this direction, enters the user's eyes, and is reflected, for example, in a direction that corresponds to the user's line of sight.
Near-infrared light reflected by the user's eyes is incident on a sensor (not shown) and photometry is performed, for example, for eye tracking.

As described above, in this example as well, the polarization state of the visible light that first enters the reflective polarizer and the polarization state of the infrared light that first enters the reflective polarizer are orthogonal to each other.
Therefore, similar to the head-mounted display 1A shown in Figure 1, visible light is magnified by the pancake lens optical system and becomes visible to the user, but near-infrared light passes through, making it possible to perform sensing such as eye tracking and iris authentication with high accuracy.

FIG. 5 is a diagram conceptually showing another example of a head-mounted display, which is a modification of the second embodiment.
5 , the near-infrared light emitting mechanism 5 may be disposed on a side surface of the display 2. Even in this case, the head mounted display 1E has, similarly to the above, a first linear polarizer 8 corresponding to the display 2 and the near-infrared light emitting mechanism 5, a near-infrared light linear polarizer 12 between the first linear polarizer 8 and the linearly polarized reflective polarizer 4, and a first λ/4 retardation plate 6.
When the near-infrared light emitting mechanism 5 is disposed on the side surface of the display 2, the near-infrared linear polarizer 12 may be formed only on the optical path of the near-infrared light emitted by the near-infrared light emitting mechanism 5. In other words, the near-infrared linear polarizer 12 may be formed by patterning another optical member on the optical path of the near-infrared light.
The operation of the head mounted display 1E in FIG. 5 is similar to the operation of the head mounted display 1D in FIG.

Fig. 6 is a conceptual diagram showing another example of a head-mounted display, which is a modification of the second embodiment. The head-mounted display 1F in Fig. 6 uses a circularly polarized reflective polarizer as the reflective polarizer.
The head-mounted display 1F in Figure 6 has a near-infrared light emitting mechanism 5, a display 2, a first linear polarizer 8, a near-infrared linear polarizer 12, an optional first λ/4 retardation plate 6, a half mirror 3, a circularly polarized reflective polarizer 10, an optional second λ/4 retardation plate 7, and an optional second linear polarizer 9.
As described above, the near-infrared linear polarizer 12 is a linear polarizer that has a polarization degree for near-infrared light of wavelength λ1 but no polarization degree for visible light, and has a transmission axis perpendicular to the plane of the drawing. Also in this example, the first linear polarizer 8 is preferably a linear polarizer that has no polarization degree in the near-infrared light region or has a small polarization degree in the near-infrared light region.

The operation of the head mounted display 1F of FIG. 6 will be described.
In the head-mounted display 1F shown in Figure 6, as in the example shown in Figure 4, visible light emitted from the display 2 passes through the first linear polarizer 8 and becomes linearly polarized light in the up and down direction in the figure, passes through the infrared linear polarizer 12, which has no polarization degree for visible light, without changing its polarization state, and passes through the first λ/4 retardation plate 6 to be converted into right-handed circularly polarized light.
The right-handed circularly polarized visible light passes through the half mirror 3 and the lens, and then enters the circularly polarized reflective polarizer 10 (initial incidence). As described above, the circularly polarized reflective polarizer 10 is a reflective polarizer that reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the right-handed circularly polarized visible light is reflected by the circularly polarized reflective polarizer 10.
As before, the right-handed circularly polarized visible light reflected by the circularly polarized reflective polarizer 10 passes through the lens and enters the half mirror 3, where half of the light is reflected. Furthermore, during this reflection, the right-handed circularly polarized visible light becomes left-handed circularly polarized light.
The left-handed circularly polarized visible light reflected by the half mirror 3 is incident again on the circularly polarized reflective polarizer 10. As described above, the circularly polarized reflective polarizer 10 reflects right-handed circularly polarized light and transmits left-handed circularly polarized light, so the left-handed circularly polarized visible light is transmitted through the circularly polarized reflective polarizer 10.
The left-handed circularly polarized visible light transmitted through the circularly polarized light reflective polarizer 10 is incident on the second λ/4 retardation plate 7 and converted into linearly polarized light in the direction perpendicular to the paper surface.
The visible light converted into linearly polarized light perpendicular to the plane of the paper by the second λ/4 phase difference plate 7 passes through the second linear polarizer 9, which transmits linearly polarized light in this direction, and is visible to the user, as before.

On the other hand, in the head-mounted display 1F of Figure 6, the near-infrared light (near-infrared light with wavelength λ1) emitted from the near-infrared light emitting mechanism 5 passes through the first linear polarizer 8 as is, as in the example shown in Figure 4, and is converted into linearly polarized light perpendicular to the paper surface by the near-infrared linear polarizer 12 having a polarization degree for the near-infrared light.
The near-infrared light, which is linearly polarized in a direction perpendicular to the paper surface, then passes through the first λ/4 retardation plate 6 and is converted into left-handed circularly polarized light.
The left-handed circularly polarized near-infrared light passes through the half mirror 3 and the lens, and then enters the circularly polarized reflective polarizer 10 (initial incidence). As described above, the circularly polarized reflective polarizer 10 is a reflective polarizer that reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the left-handed circularly polarized near-infrared light passes through the circularly polarized reflective polarizer 10.
Here, as described above, the visible light emitted from the display 2 is right-handed circularly polarized light when it first enters the circularly polarized reflective polarizer 10. That is, also in the head-mounted display 1F shown in Fig. 6 , the polarization state of the visible light that first enters the circularly polarized reflective polarizer 10 and the polarization state of the near-infrared light that first enters the circularly polarized reflective polarizer 10 are orthogonal to each other.

The left-handed circularly polarized near-infrared light transmitted through the circularly polarized light reflective polarizer 10 is incident on the second λ/4 retardation plate 7 and converted into linearly polarized light in the direction perpendicular to the paper surface.
The near-infrared light converted into linearly polarized light perpendicular to the paper surface by the second λ/4 phase difference plate 7 passes through the second linear polarizing plate 9 that transmits linearly polarized light in this direction, enters the user's eye, and is reflected, for example, in a direction corresponding to the user's line of sight.
Near-infrared light reflected by the user's eyes is incident on a sensor (not shown) and photometry is performed, for example, for eye tracking.

As described above, in this example as well, the polarization state of the visible light that first enters the reflective polarizer and the polarization state of the infrared light that first enters the reflective polarizer are orthogonal to each other.
Therefore, similar to the head-mounted display 1A shown in Figure 1, visible light is magnified by the pancake lens optical system and becomes visible to the user, but near-infrared light passes through, making it possible to perform sensing such as eye tracking and iris authentication with high accuracy.

The members used in the second embodiment (FIGS. 4 to 6) will now be described.
In the second embodiment, the display, half mirror, linearly polarized reflective polarizer, circularly polarized reflective polarizer, λ/4 phase difference plate, and near-infrared light emitting mechanism can be the same as those in the first embodiment, so their explanation will be omitted.

<Near-infrared linear polarizing plate>
The head mounted display of the second embodiment of the present invention may include a near-infrared linear polarizer. In the present invention, the near-infrared linear polarizer is a linear polarizer that has no polarization degree for visible light but has polarization degree for near-infrared light.
Examples of such near-infrared linear polarizers that can be used include those in which a dichroic dye having absorption in the near-infrared region is adsorbed and aligned on a polyvinyl alcohol-based resin film, those in which a dichroic dye having absorption in the near-infrared region is dissolved or dispersed in a liquid crystal composition to form and fix an aligned state, those in which an iodine-based polarizer is polyenized, and those in which a wire grid is applied.
The near-infrared linear polarizing plate preferably has a single-plate transmittance of less than 50%, more preferably less than 47%, at a wavelength of 850 nm, and preferably has a single-plate transmittance of less than 55%, more preferably less than 50%, and even more preferably less than 47%, at a wavelength of 950 nm.
The single plate transmittance of the near-infrared linear polarizing plate can be measured using, for example, a polarizing film measuring device VAP-7070 manufactured by JASCO Corporation. The single plate transmittance of the near-infrared linear polarizing plate in the near-infrared wavelength region can also be measured using a light source that emits infrared light and a spectrophotometer or the like.
Furthermore, with regard to the polarization degree of the near-infrared linear polarizer, P(850) is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and particularly preferably 0.95 or more. Furthermore, P(950) is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and particularly preferably 0.95 or more. The upper limits of P(850) and P(950) are theoretically 1.00, but in practice are in the range of less than 1.00.

<Linear polarizer>
The linear polarizer may be, for example, one in which iodine or a dichroic dye having absorption in the visible range is adsorbed and aligned on a polyvinyl alcohol resin film, one in which a dichroic dye having absorption in the visible range is dissolved or dispersed in a liquid crystal composition to form and fix an aligned state, or one in which a wire grid is applied.
The linear polarizer (first linear polarizer) in the second embodiment preferably has no polarization degree in the near-infrared region or a small polarization degree in the near-infrared region. "No polarization degree in the near-infrared region or a small polarization degree in the near-infrared region" means that the polarization degree in the near-infrared region is 40% or less, preferably 20% or less, and more preferably 10% or less.

[Head-mounted display of the third embodiment]
As described above, the head-mounted display of the present invention includes a display, a pancake lens optical system having a half mirror and a reflective polarizer, and a near-infrared light emitting mechanism.
In addition to these components, a head-mounted display according to a third embodiment of the present invention has a first λ/4 retardation plate between the display and the half mirror, a second λ/4 retardation plate on the viewing side of the half mirror, and a near-infrared reflective polarizer between the first λ/4 retardation plate and the second λ/4 retardation plate that reflects one circularly polarized light of wavelength λ1 and transmits the other circularly polarized light. The viewing side of the half mirror is, in other words, the side opposite the display side of the half mirror.
A head-mounted display according to a third embodiment includes a pancake lens optical system having, in this order, a display that emits at least visible light, a half mirror, and a reflective polarizer, a near-infrared light emitting mechanism, a first λ/4 retardation plate disposed between the display and the half mirror, a second λ/4 retardation plate disposed on the viewing side of the half mirror, and a near-infrared reflective polarizer disposed between the first λ/4 retardation plate and the second λ/4 retardation plate. As described above, the near-infrared reflective polarizer is a polarizer that reflects one circularly polarized light having a wavelength λ1 and transmits the other circularly polarized light.
In the third embodiment of the present invention, the near-infrared light emitting mechanism is also disposed on the display side of the half mirror and irradiates near-infrared light of wavelength λ1 toward the reflective polarizer, and at least a portion of the reflective polarizer has a reflection band in a wavelength range that includes visible light and wavelength λ1. Furthermore, the head-mounted display of the third embodiment of the present invention is also a head-mounted display in which the polarization state of the visible light that is emitted from the display and first incident on the reflective polarizer and the polarization state of the near-infrared light that is emitted from the near-infrared light emitting mechanism and first incident on the reflective polarizer are orthogonal to each other.

The head mounted display of the third embodiment will be specifically described below with reference to FIG.
7 is a conceptual diagram illustrating an example of a head mounted display according to a third embodiment of the present invention. A head mounted display 1G shown in FIG. 7 uses a linearly polarized reflective polarizer as a reflective polarizer.
The head-mounted display 1G in Figure 7 has a near-infrared light emitting mechanism 5, a display 2, an optional first linear polarizer 8, a first λ/4 retardation plate 6, a near-infrared reflective polarizer 13, a half mirror 3, a second λ/4 retardation plate 7, a linearly polarized reflective polarizer 4, and an optional second linear polarizer 9.
In this embodiment, the position of the near-infrared reflective polarizer 13 is not limited to the position shown in the illustration, and various positions can be used as long as it is between the first λ/4 retardation plate 6 and the second λ/4 retardation plate 7. In this respect, the same applies to the embodiments shown in Figs.

The operation of the head mounted display 1G in FIG. 7 will be described.
7, similarly to the first embodiment shown in Fig. 1, visible light emitted from the display 2 passes through the first linear polarizer 8 and becomes linearly polarized light in the vertical direction in the figure. In this example, the visible light that is linearly polarized in the vertical direction in the figure then passes through the first λ/4 retardation plate 6 and is converted into right-handed circularly polarized light.
The visible light, which is right-handed circularly polarized light, then enters the near-infrared reflective polarizer 13. As described above, the near-infrared reflective polarizer 13 is a polarizer that reflects one circularly polarized light of wavelength λ1 and transmits the other circularly polarized light. Therefore, the polarization of the visible light does not change even when it passes through the near-infrared reflective polarizer 13, and it remains right-handed circularly polarized light.
The right-handed circularly polarized visible light passes through the half mirror 3 and the lens, and then passes through the second λ/4 retardation plate 7, where it is converted into linearly polarized light in the vertical direction in the figure, as in the above example, and enters the linearly polarized reflective polarizer 4 (initial incidence). As described above, the linearly polarized reflective polarizer 4 is a reflective polarizer that reflects linearly polarized light in the vertical direction in the figure and transmits linearly polarized light perpendicular to the paper surface. Therefore, the visible light that is linearly polarized in the vertical direction in the figure is reflected by the linearly polarized reflective polarizer 4. The visible light that is linearly polarized in the vertical direction in the figure and reflected by the linearly polarized reflective polarizer 4 passes through the second λ/4 retardation plate 7 and is converted into right-handed circularly polarized light.
The right-handed circularly polarized visible light passes through the lens and enters the half mirror 3, where half of the light is reflected. The right-handed circularly polarized visible light becomes left-handed circularly polarized light through this reflection.
The visible light that has been reflected by the half mirror 3 and turned into left-handed circularly polarized light is converted into linearly polarized light in a direction perpendicular to the plane of the paper by the second λ/4 retardation plate 7. The visible light that has been converted into linearly polarized light in a direction perpendicular to the plane of the paper passes through the linearly polarized reflective polarizer 4.
Visible light that is linearly polarized in a direction perpendicular to the paper surface and that has passed through the linearly polarized reflective polarizer 4 passes through the second linear polarizer 9 that transmits light that is linearly polarized in this direction, and is visible to the user.

7, the near-infrared light (near-infrared light with wavelength λ1) emitted from the near-infrared light emitting mechanism 5 similarly passes through the first linear polarizer 8 to become linearly polarized light in the up-down direction in the figure, and then passes through the first λ/4 retardation plate 6, where most of the light is converted to right-handed circularly polarized light. However, because the first λ/4 retardation plate 6 does not function as a perfect λ/4 retardation plate in the near-infrared wavelength range due to its wavelength dispersion characteristics, part of the near-infrared light becomes left-handed circularly polarized light.
The near-infrared light then enters the near-infrared reflective polarizer 13. As described above, the near-infrared reflective polarizer 13 is a reflective polarizer that reflects one circularly polarized light of wavelength λ1 and transmits the other circularly polarized light. In this example, the near-infrared reflective polarizer 13 reflects right-handed circularly polarized light of wavelength λ1 and transmits left-handed circularly polarized light. Therefore, the left-handed circularly polarized component of the near-infrared light passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light. Furthermore, the right-handed circularly polarized component of the near-infrared light is reflected by the near-infrared reflective polarizer 13, and a portion of it is further reflected by the surface of the first λ/4 retardation plate 6 or the like and converted into left-handed circularly polarized light, which then passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light.
Furthermore, when the first linear polarizer 8 is a polarizer that does not have a polarization degree in the near-infrared light region or has a small polarization degree in the near-infrared light region, the near-infrared light emitted from the near-infrared light emitting mechanism 5 enters the near-infrared reflective polarizer 13 as unpolarized light. A left-handed circularly polarized component of the near-infrared light passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light. A right-handed circularly polarized component of the near-infrared light is reflected by the near-infrared reflective polarizer 13, and a portion of the right-handed circularly polarized light is further reflected by the surface of the first λ/4 retardation plate 6 or the like and converted into left-handed circularly polarized light, which then passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light.
The left-handed circularly polarized near-infrared light passes through the half mirror 3 and the lens, and then passes through the second λ/4 retardation plate 7. As in the above example, the light is converted into linearly polarized light perpendicular to the plane of the paper, and enters the linearly polarized reflective polarizer 4 (initial incidence). As described above, the linearly polarized reflective polarizer 4 is a reflective polarizer that reflects linearly polarized light in the up-down direction in the figure and transmits linearly polarized light perpendicular to the plane of the paper. Therefore, the near-infrared light that is linearly polarized perpendicular to the plane of the paper passes through the linearly polarized reflective polarizer 4.
Here, as described above, the visible light emitted from the display 2 is linearly polarized in the up-down direction in the drawing when it first enters the linearly polarized reflective polarizer 4. That is, also in the head-mounted display 1G shown in Fig. 7, the polarization state of the visible light that first enters the linearly polarized reflective polarizer 4 and the polarization state of the near-infrared light that first enters the linearly polarized reflective polarizer 4 are orthogonal to each other.

The near-infrared light that is linearly polarized in a direction perpendicular to the paper surface and that passes through the linearly polarized reflective polarizer 4 passes through the second linear polarizer 9 that transmits linearly polarized light in this direction, enters the user's eyes, and is reflected, for example, in a direction that corresponds to the user's line of sight.
Near-infrared light reflected by the user's eyes is incident on a sensor (not shown) and photometry is performed, for example, for eye tracking.

As described above, in this example as well, the polarization state of the visible light that first enters the reflective polarizer and the polarization state of the infrared light that first enters the reflective polarizer are orthogonal to each other.
Therefore, similar to the head-mounted display 1A shown in Figure 1, visible light is magnified by the pancake lens optical system and becomes visible to the user, but near-infrared light passes through, making it possible to perform sensing such as eye tracking and iris authentication with high accuracy.

FIG. 8 is a diagram conceptually showing another example of a head-mounted display, which is a modification of the third embodiment.
8 , the near-infrared light emitting mechanism 5 may be disposed on the side surface of the display 2. In this case, the head mounted display 1H also has a first linear polarizing plate 8 corresponding to the display 2 and the near-infrared light emitting mechanism 5, and a near-infrared reflective polarizer 13 between the λ/4 retardation plate 6 and the λ/4 retardation plate 7, as in the previous case.
When the near-infrared light emitting mechanism 5 is disposed on the side surface of the display 2, the near-infrared reflective polarizer 13 may be formed only on the optical path of the near-infrared light emitted by the near-infrared light emitting mechanism 5. In other words, the near-infrared reflective polarizer 13 may be formed by patterning another optical member on the optical path of the near-infrared light.
The operation of the head mounted display 1H in FIG. 8 is similar to the operation of the head mounted display 1G in FIG.

Fig. 9 is a conceptual diagram showing another example of a head mounted display, which is a modification of the third embodiment. The head mounted display 1I in Fig. 9 uses a circularly polarized reflective polarizer as the reflective polarizer.
The head-mounted display 1I in Figure 9 has a near-infrared light emitting mechanism 5, a display 2, an optional first linear polarizer 8, a first λ/4 retardation plate 6, a near-infrared reflective polarizer 13, a half mirror 3, a circularly polarized light reflective polarizer 10, a second λ/4 retardation plate 7, and an optional second linear polarizer 9.
As described above, the near-infrared reflective polarizer 13 is a reflective polarizer that reflects one circularly polarized light of wavelength λ1 and transmits the other circularly polarized light.

The operation of the head mounted display 1I in FIG. 9 will be described.
In the head-mounted display 1I shown in Figure 9, as in the example shown in Figure 7, visible light emitted from the display 2 passes through the first linear polarizer 8 to become linearly polarized light in the up and down direction in the figure, and then passes through the first λ/4 retardation plate 6 to be converted into right-handed circularly polarized light.
The visible light, which is right-handed circularly polarized light, then enters the near-infrared reflective polarizer 13. As described above, the near-infrared reflective polarizer 13 is a polarizer that reflects one circularly polarized light of wavelength λ1 and transmits the other circularly polarized light. Therefore, the polarization of the visible light does not change even when it passes through the near-infrared reflective polarizer 13, and it remains right-handed circularly polarized light.
The right-handed circularly polarized visible light passes through the half mirror 3 and the lens, and then enters the circularly polarized reflective polarizer 10 (initial incidence). As described above, the circularly polarized reflective polarizer 10 is a reflective polarizer that reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the right-handed circularly polarized visible light is reflected by the circularly polarized reflective polarizer 10.
As before, the right-handed circularly polarized visible light reflected by the circularly polarized reflective polarizer 10 passes through the lens and enters the half mirror 3, where half of the light is reflected. Furthermore, during this reflection, the right-handed circularly polarized visible light becomes left-handed circularly polarized light.
The left-handed circularly polarized visible light reflected by the half mirror 3 is incident again on the circularly polarized reflective polarizer 10. As described above, the circularly polarized reflective polarizer 10 reflects right-handed circularly polarized light and transmits left-handed circularly polarized light, so the left-handed circularly polarized visible light is transmitted through the circularly polarized reflective polarizer 10.
The left-handed circularly polarized visible light transmitted through the circularly polarized light reflective polarizer 10 is incident on the second λ/4 retardation plate 7 and converted into linearly polarized light in the direction perpendicular to the paper surface.
The visible light converted into linearly polarized light perpendicular to the plane of the paper by the second λ/4 phase difference plate 7 passes through the second linear polarizer 9, which transmits linearly polarized light in this direction, and is visible to the user, as before.

9, the near-infrared light (near-infrared light with wavelength λ1) emitted from the near-infrared light emitting mechanism 5 similarly passes through the first linear polarizer 8 to become linearly polarized light in the up-down direction in the figure, and then passes through the first λ/4 retardation plate 6, where most of the light is converted to right-handed circularly polarized light. However, because the first λ/4 retardation plate 6 does not function as a perfect λ/4 retardation plate in the near-infrared wavelength range due to its wavelength dispersion characteristics, part of the near-infrared light becomes left-handed circularly polarized light.
The near-infrared light then enters the near-infrared reflective polarizer 13. As described above, the near-infrared reflective polarizer 13 is a reflective polarizer that reflects one circularly polarized light of wavelength λ1 and transmits the other circularly polarized light. In this example, the near-infrared reflective polarizer 13 reflects right-handed circularly polarized light of wavelength λ1 and transmits left-handed circularly polarized light. Therefore, the left-handed circularly polarized component of the near-infrared light passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light. Furthermore, the right-handed circularly polarized component of the near-infrared light is reflected by the near-infrared reflective polarizer 13, and a portion of it is further reflected by the surface of the first λ/4 retardation plate 6 or the like and converted into left-handed circularly polarized light, which then passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light.
Furthermore, when the first linear polarizer 8 is a polarizer that does not have a polarization degree in the near-infrared light region or has a small polarization degree in the near-infrared light region, the near-infrared light emitted from the near-infrared light emitting mechanism 5 enters the near-infrared reflective polarizer 13 as unpolarized light. A left-handed circularly polarized component of the near-infrared light passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light. A right-handed circularly polarized component of the near-infrared light is reflected by the near-infrared reflective polarizer 13, and a portion of the right-handed circularly polarized light is further reflected by the surface of the first λ/4 retardation plate 6 or the like and converted into left-handed circularly polarized light, which then passes through the near-infrared reflective polarizer 13 and becomes left-handed circularly polarized light that is orthogonal to visible light.
The left-handed circularly polarized near-infrared light passes through the half mirror 3 and the lens, and then enters the circularly polarized reflective polarizer 10 (initial incidence). As described above, the circularly polarized reflective polarizer 10 is a reflective polarizer that reflects right-handed circularly polarized light and transmits left-handed circularly polarized light. Therefore, the left-handed circularly polarized near-infrared light passes through the circularly polarized reflective polarizer 10.
Here, as described above, the visible light emitted from the display 2 is right-handed circularly polarized light when it first enters the circularly polarized reflective polarizer 10. That is, also in the head-mounted display 1I shown in Fig. 9 , the polarization state of the visible light that first enters the circularly polarized reflective polarizer 10 and the polarization state of the near-infrared light that first enters the circularly polarized reflective polarizer 10 are orthogonal to each other.

The left-handed circularly polarized near-infrared light transmitted through the circularly polarized light reflective polarizer 10 is incident on the second λ/4 retardation plate 7 and converted into linearly polarized light in the direction perpendicular to the paper surface.
The near-infrared light converted into linearly polarized light perpendicular to the paper surface by the second λ/4 phase difference plate 7 passes through the second linear polarizing plate 9 that transmits linearly polarized light in this direction, enters the user's eye, and is reflected, for example, in a direction corresponding to the user's line of sight.
Near-infrared light reflected by the user's eyes is incident on a sensor (not shown) and photometry is performed, for example, for eye tracking.

As described above, in this example as well, the polarization state of the visible light that first enters the reflective polarizer and the polarization state of the infrared light that first enters the reflective polarizer are orthogonal to each other.
Therefore, similar to the head-mounted display 1A shown in Figure 1, visible light is magnified by the pancake lens optical system and becomes visible to the user, but near-infrared light passes through, making it possible to perform sensing such as eye tracking and iris authentication with high accuracy.

The components used in the third embodiment (Figures 7 to 9) will be described. Note that the display, half mirror, linearly polarized reflective polarizer, circularly polarized reflective polarizer, λ/4 retardation plate, linear polarizer, and near-infrared light emission mechanism can be the same as those in the first embodiment, so their description will be omitted.

<Near infrared reflective polarizer>
The head-mounted display of the present invention may have a near-infrared reflective polarizer. The near-infrared reflective polarizer reflects one circularly polarized light of wavelength λ1 (near-infrared light) and transmits the other circularly polarized light. Furthermore, it is preferable that the near-infrared reflective polarizer does not have a reflection band in the visible light region.
As a near-infrared reflective polarizer that reflects one circularly polarized light of near-infrared light and transmits the other circularly polarized light, and does not have a reflection band in the visible light region, for example, a rod-shaped liquid crystal compound or a discotic liquid crystal compound that is cholesterically oriented can be used.

The head-mounted display of the present invention has been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may of course be made without departing from the spirit of the present invention.

1A to 1I Head-mounted display 2 Display 3 Half mirror 4 Linearly polarized reflective polarizer 5 Near-infrared light emission mechanism 6 First λ/4 retardation plate 7 Second λ/4 retardation plate 8 First linear polarizer 9 Second linear polarizer 10 Circularly polarized reflective polarizer 11 Optical function layer 12 Near-infrared linear polarizer 13 Near-infrared reflective polarizer

Claims (6)

a pancake lens optical system having, in this order, a display that emits at least visible light, a half mirror, and a reflective polarizer;
a near-infrared light emitting mechanism,
the near-infrared light emitting mechanism is disposed on the display side of the half mirror, and irradiates near-infrared light having a wavelength λ1 toward the reflective polarizer;
the reflective polarizer has a reflection band in a wavelength range that includes at least a portion of the visible light and the wavelength λ1,
a polarization state of the visible light emitted from the display and first incident on the reflective polarizer and a polarization state of the near-infrared light emitted from the near-infrared light emitting mechanism and first incident on the reflective polarizer are orthogonal to each other;
Head-mounted display. The head-mounted display of claim 1, wherein the reflective polarizer has a curved shape. a first linear polarizer is disposed between the display and the half mirror;
3. The head-mounted display according to claim 1, further comprising an optical functional layer between the first linear polarizer and the reflective polarizer, the optical functional layer having a phase difference of ½ wavelength with respect to near-infrared light of wavelength λ1 and no phase difference with respect to visible light. The head-mounted display of claim 3, wherein the optical function layer includes at least a layer formed by curing a rod-shaped liquid crystal compound and a layer formed by curing a discotic liquid crystal compound. a first linear polarizer is disposed between the display and the half mirror;
3. The head-mounted display of claim 1, further comprising a linear polarizer between the first linear polarizer and the reflective polarizer, the linear polarizer having a polarization degree for near-infrared light of wavelength λ1 and no polarization degree for visible light. a first λ/4 retardation plate between the display and the half mirror;
a second λ/4 phase difference plate on the viewing side of the half mirror;
3. The head-mounted display according to claim 1, further comprising a near-infrared reflective polarizer between the first λ/4 retardation plate and the second λ/4 retardation plate, the near-infrared reflective polarizer reflecting one circularly polarized light of the wavelength λ1 and transmitting the other circularly polarized light.