CA2828407A1

CA2828407A1 - Light control in head mounted displays

Info

Publication number: CA2828407A1
Application number: CA2828407A
Authority: CA
Inventors: John N. Border; Joseph Bietry; John D. Haddick; Robert Michael Lohse
Original assignee: Osterhout Group Inc
Current assignee: Microsoft Technology Licensing LLC
Priority date: 2011-02-28
Filing date: 2012-01-25
Publication date: 2012-09-07
Also published as: WO2012118573A1; DE112012001032T5; CA2828413A1; WO2012118575A2; DE112012001022T5; WO2012118575A3

Abstract

A see-through head mounted display apparatus with reduced eyeglow is disclosed. Two images of a scene are combined and presented to a user, the combined image including portions of reflected image light and light from a see- through view of an external environment. The apparatus includes a light control element to block escaping portions of image light and reflected portions of scene light, while allowing incoming scene light to be transmitted from the external environment. The images are produced using a partially reflecting mirror and a light control element. A portion of scene light is transmitted through the partially reflecting mirror and is combined with a portion of image light reflected from the partially reflecting mirror. A light control element is used to block a portion of the image light and a portion of the scene light to reduce eyeglow.

Description

LIGHT CONTROL IN HEAD MOUNTED DISPLAYS
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of and claims priority to U.S. Pat. Appl. 13/037,324, filed 28 February 2011, now U.S. Pat. No. , and to U.S. Pat. Appl. 13/037,335, also filed on 28 February 2011, now U.S. Pat. No.
_____ , both of which are hereby incorporated by reference in their entirety.
FIELD OF THE INVENTION

[0002] The present disclosure pertains to see-through head mounted displays and the control of light entering and exiting the head mounted display.
BACKGROUND

[0003] See-through head mounted displays allow a user to view a displayed image or a see-through view of the scene in front of the user. See-through head mounted displays can also allow the user to view a combined image comprised of a displayed image and a see-through view of the scene in front of the user in which the displayed image is overlaid on the see-through view. In different modes of operation, the see-through head mounted display can present the displayed image so that the area of the displayed image is transparent, semitransparent or opaque. In the transparent mode, the see-through view of the scene is unblocked and an overlaid displayed image can be provided with low contrast. In the semitransparent mode, the see-through view of the scene is partially blocked and an overlaid displayed image can be provided with higher contrast. In the opaque mode, the se-through view of the scene is fully blocked and an overlaid displayed image can be provided with high contrast.

[0004] Alternatively, some head-mounted displays provide a see-through display for an augmented reality view in which real-world scenes are visible to a user but additional image information is overlaid on the real-world scenes. Such an augmented reality view is provided by helmet mounted see-through displays found in military applications and by heads-up displays (HUDs) in the windshields of automobiles. In this case, there can be multiple areas for displaying images over the see-through view.

[0005] U.S. Pat. No. 5151722 describes a head mounted display with a folded optical path and a beam splitter with a curved mirror to present an image from a CRT
image source to the user's eye. The image source is positioned on the side of the user's head with the optical path multiply folded to present the image light from the image source into the user's eye. The curved mirror is positioned between the user's eye and the scene in front of the user. A see-through version of the head mounted display is also discussed wherein the curved mirror is a partially reflective mirror so the user can see through the curved mirror to view the scene in front of the user.
However, the CRT image source is large and heavy so that it is not well suited for head mounted displays. The multiply folded geometry with the image source located on the side of the user's head makes for a larger beam splitter and a thicker geometry in front of the user's eye so that the overall size of the head mounted display is larger.
Image light that passes through the partially reflecting mirror is uncontrolled and as such, a portion of the image light escapes through the front of the see-through head mounted display and is seen externally as eyeglow.

[0006] U.S. Pat. No. 5699194 discloses a see-through head mounted display with a waveguide wherein the outer surface is a partially reflecting mirror. In this see-through head mounted display, image light from the image source is reflected multiple times from different areas of the partially reflecting mirror before the image light is presented to the user's eye. In addition, a corrective lens is provided so that distortions of the see-through view of the scene are reduced. And, a liquid crystal shutter is provided to block incoming light from the scene so that the see-through headmounted display can be operated in an opaque mode. Image light that passes through the partially reflecting mirror is uncontrolled and as such, a portion of the image light escapes through the front of the see-through head mounted display and is seen externally as eyeglow.

[0007] U.S. Pat. No. 6693749 describes a head mounted display with a polarizing beam splitter cube to reduce light losses and improve efficiency. An image source is positioned above the user's eye and the optical path is folded once to present the image light from the image source to the user's eye. A curved fully reflecting mirror is positioned below the user's eye to focus the image light at the user's eye.
An unpolarized image source is used so that half of the image light from the image source passes through the polarizing beam splitter while the other half of the light is reflected away from the user's eye and toward the scene in front of the user. A
polarizer is positioned in front of the polarizing beam splitter cube to block the half of the light that is reflected away from the user's eye and thereby make the user less observable by others in the neighboring environment. However, the polarizing beam splitter cube is large and heavy, so that it is not well suited for use in a head mounted display.
Further, the curved mirror is also relatively large so that by locating the mirror below the user's eye, the thickness of the see-through head mounted display is necessarily larger.

[0008] There is a need, therefore, for an improved see-through head-mounted display that provides a thinner, lighter weight display which also controls escaping light to reduce eyeglow.
SUMMARY

[0009] The present disclosure provides a see-through head mounted display that is thin and light in weight with a light control element to selectively block escaping image light and thereby reduce eyeglow.

[0010] In one embodiment, a see-through head mounted display apparatus is provided. The see-through head mounted display apparatus includes a see-through display assembly including an image source and a partially reflecting mirror.
The partially reflecting mirror reflects and transmits respective portions of image light from the image source and scene light from a see-through view of an external environment. A combined image comprised of portions of the reflected image light and the transmitted scene light is provided to a user's eye. A light control element is provided to block escaping light comprised of the transmitted portion of image light and the reflected portion of scene light, while allowing a portion of incoming scene light to be transmitted from the external environment to the see-through display assembly. The light control element transmits a higher percentage of incoming scene light than the percentage of escaping light that is not blocked.

[0011] In another embodiment, a method for viewing an image with reduced eyeglow on a see-through head mounted display having a front and a back is provided. The method includes steps of providing image light to a partially reflecting mirror from an image displayed on an image source and reflecting a first portion of the image light from the partially reflecting mirror while transmitting a second portion of the image light through the partially reflecting mirror. The method also includes steps of transmitting a first portion of scene light from the external environment through a light control element at the front of the see-through head mounted display.
Additional steps include transmitting a second portion of the scene light through the partially reflecting mirror while reflecting a third portion of the scene light from the partially reflecting mirror, and combining the first portion of the image light with the second portion of the scene light to provide a combined image to a viewer's eye at the back of the see-through head mounted display comprised of the image displayed on the image source overlaid on a view of the external environment. The method also includes a step of using the light control element to block the transmitted second portion of the image light and the reflected third portion of the scene light to reduce eyeglow.
BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is an illustration of a see-through head mounted display device;

[0013] FIG. lA is an illustration of a user with a see-through head mounted display device wherein eyeglow is depicted;

[0014] FIG. 2 is an illustration of a combination image as seen by a user when the see-through display device is operated in a transparent mode;

[0015] FIG. 3 is an illustration of a combination image as seen by a user when the see-through display device is operated in a semi-transparent mode;

[0016] FIG. 4 is a schematic view of a cross-section of a see-through display assembly;

[0017] FIG. 5 is a schematic view of a cross-section of a see-through display assembly;

[0018] FIG. 6 is an illustration of an example of the polarization control used to reduce eyeglow;

[0019] FIG. 7 is a schematic cross-section of a light control element;

[0020] FIG. 8 is a schematic cross-section of a see-through display assembly with a light control element mounted in a glasses frame; and

[0021] FIG. 9 is a flowchart describing a method disclosed herein.
DETAILED DESCRIPTION

[0022] In a see-through head mounted display, a displayed image can be viewed by a user at the same time that a see-through view of the scene from the surrounding environment can be viewed. The displayed image and the see-through view can be viewed as a combined image where the displayed image is overlaid on the see-through view or the displayed image and the see-through view can be simultaneously viewed in different portions of the see-through display that are viewable by the user.

[0023] FIG. 1 shows an illustration of a see-through head mounted display device 100. The device includes a frame 105 with lenses 110 that have display areas 115 and clear areas 102. The device also has image sources and associated optics (not shown) to present image light from the image source to the display areas 115, wherein the image sources and associated optics can be located at the top, bottom or side of the display areas 115. The frame 105 is supported on the viewer's head with arms 130. The arms 130 also contain electronics 125 including a processor to drive the displays and peripheral electronics 127 including batteries and wireless connection(s) to other information sources such as can be obtained on the intern& or from localized servers through Wi-Fi, Bluetooth, cellular or other wireless technologies. A
camera 120 can be included to capture images of the surrounding environment. The locations of the various components in the see-through head mounted display device 100 are shown as an example, other locations are possible.

[0024] The see-through head-mounted display device 100 can further include controllable darkening layers in the display areas 115 wherein the controllable darkening layers can change opacity behind the respective portions of the display area 115 to enable changes in operating mode between transparent, semi-transparent and opaque in the areas where images are displayed. The controllable darkening layers can be segmented so that images can be displayed over different areas of the lenses 110. FIG. 2 shows an example of a combined image as seen by a user using a see-through head mounted display device 100 wherein the see-through head mounted display device 100 is operating in a transparent mode. As can be seen in FIG.
2, the displayed image seen by the user has a low contrast and objects from the see-through view are easily seen in the display area 115. FIG. 3 shows an example of a combined image as seen by a user using a see-through head mounted display device 100 wherein the see-through head mounted display device 100 is operating in a semi-transparent mode. As can be seen in FIG. 3, the displayed image seen by the user has a higher contrast and objects from the see-through view are very dim in the display area 115.

[0025] A wide variety of see-through head mounted display devices 100 are known in the art. See-through head-mounted display devices 100 can provide image information to one eye of the user or both eyes of the user. See-through head mounted display devices 100 that present image information to both eyes of the user can have one or two image sources. Monoscopic viewing in which the same image information is presented to both eyes is done with see-through head mounted display devices 100 that have one or two image sources. Stereoscopic viewing typically requires a head-mounted display device 100 that has two image sources with different images being presented to the user's eyes wherein the different images have different perspectives of the same scene.

[0026] A variety of image sources to provide images for display are known in the art including, for example, organic light-emitting diode (OLED) displays, quantum dot based light emitting diodes (QLED) displays, liquid crystal displays (LCDs), or liquid crystal on silicon (LCOS) displays. In addition, the image sources can be microprojectors or microdisplays with associated optics to present the image light to the display areas 115 so that the user can view the displayed images with his/her eyes.

[0027] The optics associated with the image sources relay the image light from the image sources to the display areas 115. The optics can comprise refractive lenses, reflective lenses, mirrors, diffractive lenses, holographic lenses or waveguides. For a see-through head mounted display device 100, the user should be provided with at least a partial view of the scene in front of the see-through head-mounted display device 100 within the user's field of view. The present disclosure concerns see-through head mounted display devices 100 that have optics associated with the image source that include a partially reflective mirror for simultaneously presenting image light and scene light to the user so that the user is provided with a displayed image overlaid on at least a partial see-through view of the scene in front of the user.
Wherein the partially reflective mirror can be any type of reflecting mirror surface that also allows some portion of the incident light to be transmitted such as for example a partially metalized coated surface or a dielectric multilayer mirror coated surface.

[0028] When using a see-through head mounted display, light losses from the display areas 115 and from light reflected or scattered from the image source or associated optics or light reflected or scattered from the user, contribute light that passes from the see-through head mounted display into the environment. These light losses are perceived by external viewers as eyeglow where portions of the lenses 110 or the areas surrounding the see-through head mounted display device 100 appear to be glowing when viewed in a dimly lit environment. In certain cases of eyeglow as shown in FIG. 1A, the displayed image can be seen as an observable image 190 in the display areas 115 when viewed externally by external viewers. To maintain privacy of the viewing experience for the user both in terms of maintaining privacy of the images being viewed and in terms of making the user less noticeable when using the see-through head mounted display device 100 in a dimly lit environment, it is preferable to reduce eyeglow. This disclosure provides methods and apparatus that reduce eyeglow in see-through head mounted displays such as the see-through head mounted display devices 100 which include a partially reflective mirror in the optics associated with the image source.

[0029] FIGS. 4 and 5 provide examples of optics associated with image sources for see-through head mounted display devices 100 that include partially reflective mirrors 440 and 540. Light control elements 480 and 580 block image light that passes through the partially reflective mirrors 440 and 540 respectively to reduce escaping light that contributes to eyeglow.

[0030] Turning first to FIG. 4, the optics associated with the image source in this example will be described. In this example, the image source includes a projection system (not shown) to provide image light with an optical layout that includes a first horizontal optical axis located in or along the upper portion of the frame 105 in the see-through head mounted display device 100. The optics along this first horizontal axis can include lenses to focus the image light 470 to provide a focused displayed image from the image source to the user's eye 410. A folding mirror 460 then redirects the image light 470 from the first horizontal axis to a non-vertical optical axis 452 that proceeds to a see-through display assembly 400 with a beam splitter layer 420 and a second horizontal optical axis 450. The beam splitter layer 420 can be a partially reflecting mirror or a polarizing beam splitter layer. The beam splitter layer 420 in the see-through display assembly 400 is oriented at an angle to the non-vertical optical axis and the second horizontal optical axis 450 to provide a thinner see-through display assembly 400. The beam splitter layer 420 reflects and redirects at least a portion of the image light 470 along the second horizontal optical axis 450 in a direction away from the user's eye 410. A first portion of the image light 470 that has been reflected by the beam splitter layer 420, is then reflected back toward the user's eye 410 by a partially reflecting mirror 440. The partially reflecting mirror 440 can be spherical or aspheric as appropriate to present a focused image to the user's eye 410. The reflected first portion of the image light 470 then passes back through the beam splitter and is focused at the user's eye 410.

[0031] At the same time, a second portion of the image light 470 that has been reflected by the beam splitter layer 420, is transmitted through the partially reflecting mirror 440. It is this second portion of image light 470 that escapes from the see-through display assembly 400 to contribute to eyeglow in the form of an observable image 190 that can be seen by external viewers. Light control element 480 blocks the second portion of the image light 470 thereby reducing escaping light and reducing eyeglow. In one embodiment, the light control element 480, the partially reflecting mirror 440, the beam splitter layer 420 and the user's eye 410 are all located along a common optical axis, the second horizontal optical axis 450.
Simultaneously, a first portion of scene light from the external environment 465 passes through the light control element 480. A second portion of the scene light 465 then passes through the partially reflective mirror 440 and the beam splitter layer 420 to combine with the first portion of the image light 470 to present a combined image to the user's eye 410. The combined image includes the displayed image from the image source overlaid onto at least a partial see-through view of the external environment in front of the user.

[0032] At the same time, a third portion of the scene light 465 is reflected by the partially reflecting mirror 440. This third portion of scene light 465 also contributes to eyeglow since it escapes from the see-through display assembly 400.
However, the third portion of scene light 465 contributes a generally reflected light from the environment and as such does not contribute to the observable image 190 that can be seen by external viewers. The eyeglow produced by the third portion of scene light 465 is seen by external viewers as a general brightness in the lenses 110 or as a reflected image of the external scene in front of the user.

[0033] In an embodiment, the image source provides linearly polarized image light 470 and the beam splitter layer 420 is a partially reflective mirror.
Linearly polarized image light can be provided by various means including microdisplays with linearly polarized illumination such as LCOS displays or LCD displays, alternately self-luminous displays (such as OLED, QLED and transmissive LCOS) with a linear polarizer can be used to provide linearly polarized image light 470. With linearly polarized image light 470 and a partially reflective mirror as the beam splitter layer 420, the light control element 480 is a linear polarizer. Wherein the linear polarizer in the light control element 480 is oriented relative to the linearly polarized image light 470 so that the second portion of the linearly polarized image light 470 that passes through the partially reflecting mirror 440 is blocked and eyeglow is reduced.

[0034] In a further embodiment, the beam splitter layer 420 is a polarizing beam splitter, or the image source provides polarized image light 470 and the beam splitter layer 420 is a polarizing beam splitter, so that the reflected image light 470 is linearly polarized light, this embodiment and the associated polarization control is shown in FIG. 6. For the case where the image source provides linearly polarized image light and the beam splitter layer 420 is a polarizing beam splitter, the polarization state of the image light is aligned to the polarizing beam splitter so that the image light 470 is reflected by the polarizing beam splitter. FIG. 6 shows the reflected image light as having S state polarization. In cases where the beam splitter layer 420 is a polarizing beam splitter, a first quarter wave film 430 is provided between the beam splitter layer 420 and the partially reflecting mirror 440.

[0035] The first quarter wave film 430 converts the linearly polarized image light to circularly polarized image light (shown as S being converted to CR in FIG.
6). The reflected first portion of image light 470 is then also circularly polarized where the circular polarization state is reversed (shown as CL in FIG. 6) so that after passing back through the quarter wave film, the polarization state of the reflected first portion of image light 470 is reversed (to P polarization) compared to the polarization state of the image light 470 provided by the image source (shown as S). As a result, the reflected first portion of the image light 470 passes through the polarizing beam splitter without reflection losses. When the beam splitter layer 420 is a polarizing beam splitter and the see-through display assembly 400 includes a first quarter wave film 430, the light control element 480 is a second quarter wave film 653 and a linear polarizer 654. Wherein the second quarter wave film 653 converts the second portion of the circularly polarized image light 470 into linearly polarized image light 470 (shown as CR being converted to S) with a polarization state that is blocked by the linear polarizer 654 in the light control element 480 so that eyeglow is reduced.

[0036] When the light control element 480 includes a linear polarizer 654 and a quarter wave film 653, incoming unpolarized scene light 465 from the external environment in front of the user is converted to linearly polarized light (shown as P
polarization state in FIG. 6) while 50% of the light is blocked. The first portion of scene light 465 that passes through the linear polarizer 654 is linearly polarized light which is converted by the quarter wave film to circularly polarized light (shown as P
being converted to CL in FIG. 6). The third portion of scene light that is reflected from the partially reflecting mirror 440 has reversed circular polarization (shown as converting from CL to CR in FIG. 6) which is then converted to linearly polarized light by the second quarter wave film 653 (shown as CR converting to S
polarization in FIG. 6). The linear polarizer 654 then blocks the reflected third portion of the scene light thereby reducing escaping light and reducing eyeglow.

[0037] As shown in FIG. 6, the reflected first portion of image light 470 and the transmitted second portion of scene light have the same circular polarization state (shown as CL) so that they combine and are converted by the first quarter wave film 430 into linearly polarized light (shown as P) which passes through the beam splitter when the beam splitter layer 420 is a polarizing beam splitter. The linearly polarized combined light 690 then provides a combined image to the user's eye 410 located at the back of the see-through display assembly 400, where the combined image is comprised of overlaid portions of the displayed image from the image source and the see-through view of the external environment in front of the user.

[0038] The example optics associated with image sources for see-through head mounted display devices 100 shown in FIG. 5 as see-through display assembly will now be addressed. In this example, an image source 520 that provides linearly polarized image light 570 is used. The linearly polarized image light 570 enters a waveguide 555 wherein the light is first reflected by total internal reflection from the back surface 530, a first portion of the image light 570 is reflected from a partially reflecting mirror 540 and then transmitted through surface 530 to present an image from the image source 520 to the user's eye 410. The user looks through the waveguide 555 and the partially reflecting mirror 540 to obtain a see-through view of the external scene in front of the user. Due to distortions imparted by the thick layers of optical material in the waveguide 555, a corrective element 560 is provided to reduce distortions in the see-through view seen by the user. The combined image presented to the user's eye 410, comprised of the displayed image from the image source 520 overlaid on at least a portion of a see-through view of the external scene, is formed from the image light 570 and the scene light 565. In this example, eyeglow comes from a second portion of image light 570 that is transmitted through the partially reflecting mirror 540 where it passes through the corrective element 560 and escapes from the see-through display assembly 500.

[0039] In this case, the linear polarization of the image light 570 is maintained so that the second portion of image light 570 that escapes from the see-through display assembly 500 has the same linear polarization as the image light 570 provided by the image source 520. The light control element 580 for this embodiment comprises a linear polarizer that is oriented along with the image source 520 so that escaping light is blocked. The polarization state of the image light 570 and the orientation of the linear polarizer in the light control element 580 are chosen together to block escaping light. As an example, if the image source 520 provides S
polarized image light 570, the linear polarizer in the light control element 580 is oriented to block S polarized light. As shown in FIG. 5, the light control element 580, the corrective element 560, the partially reflective mirror 540, the waveguide 555 and the user's eye 410 are all located on a common optical axis 550. In addition, while FIG. 5 shows image light 570 being reflected once on surface 530 and once on partially reflecting mirror 540, waveguides can be used where multiple reflections of the image light 570 occur on either the surface 530 or the partially reflective mirror 540.

[0040] It should be noted, that the embodiments may include see-through display assemblies 400 and 500 where partially reflective mirrors 440 and 540 respectively are located on common optical axes with the user's eye 410 and light control elements 480 and 580 respectively. This optical layout has been selected to provide the additional benefit of providing a thin see-through display assembly with a large displayed field of view overlaid onto the see-through field of view. To provide a large displayed field of view, the portion of the partially reflective mirror where the image is displayed must be relatively large. By including an angled beam splitter layer as shown in FIG. 4, it is possible to locate the partially reflective mirror above or below the see-through field of view. However, if the partially reflective mirror is located with an optical axis that is perpendicular to the optical axis associated with the see-through field of view, the lateral dimension of the partially reflective mirror increases the thickness of the see-through display assembly substantially.

[0041] As a result, the embodiments may include partially reflective mirrors that share an optical axis with the see-through field of view so that the large dimension of the partially reflective mirror that is associated with the large displayed field of view is vertical and as such does not contribute to the thickness of the see-through display assembly. However, since the partially reflective mirror is located on the optical axis of the see-through field of view, the partially reflective mirror must be both partially reflective to provide the displayed image and partially transparent to provide the see-through view. As an example, a see-through display assembly was designed similar to that shown in FIG. 4 for a 30 degree field of view displayed image. The partially reflective mirror was then 15 mm high. By positioning the partially reflective mirror in front of the user, the thickness of the see-through display assembly from the front of the partially reflective mirror to the back of the beam splitter layer was reduced to mm.

[0042] In a further embodiment, the light control layer includes an electrically controllable darkening layer to reduce the amount of scene light entering the see-through head mounted display. The controllable darkening layer is controlled in response to detected changes in the environment, changes in the user's movements or changes in the type of images being displayed. In one embodiment, the controllable darkening layer is segmented to provide differential control in the display areas and the clear areas of the lens to provide a displayed image with higher contrast.

Examples of controllable darkening layers include various types of liquid crystal layers, electrowetting layers or electrochromic layers.

[0043] FIG. 7 shows a cross-sectional view of a light control element 700.
Light control element 700 includes a controllable darkening layer 652, a quarter wave film 653, a linear polarizer 654 and a support layer 740. In another embodiment, light control element 700 can be a separate replaceable element in the see-through head mounted display device 100. In this way, different levels of functionality can be built into the light control element 700 such as different color tints or thicker support layers 740 to provide increased impact resistance, ballistic protection or laser protection.
Impact resistance can be provided with a high impact plastic such as polycarbonate and ballistic protection can be provided with a laminated component, as in bullet proof glass. Laser protection can also be provided, for example, with cut filters to block laser wavelengths. In a further example, the support layer 740 can include photochromic materials which automatically darken when in bright environments to block a portion of the scene light thereby making it easier to view displayed images.

[0044] In another example, the controllable darkening layer 652 can be included in some versions of the light control element 700 to block a portion of the scene light to provide improved viewing conditions with higher contrast displayed images in portions of the combined image Simpler versions of light control element 700 may simply omit the controllable darkening layer 652. As previously discussed, the quarter wave film 653 should be left out of the light control element 700 when used with certain types of see-through display assemblies 400 such as when the image source provides linearly polarized image light 470 and the beam splitter layer 420 is a partially reflective mirror or when a see-through display assembly 500 is used.

[0045] FIG. 8 shows an example of a see-through display assembly with a light control element 480 in a glasses frame. The glasses cross-section 800 shows the components of see-through display assembly 400 in a glasses frame 805.
Wherein, the light control element 480 covers the entire see-through view seen by the user.
Supporting members 887 and 885 are shown supporting the partially reflecting mirror 440 and the beam splitter layer 420 respectively in the field of view of the user's eye 410. The supporting members 885 and 887 along with the light control element are connected to the glasses frame 805. The other components such as the folding mirror 460 and the first quarter wave film 430 are also connected to the supporting members 887 and 885 so that the combined assembly is structurally sound.

[0046] FIG. 9 describes a method of using the present disclosure. In step 910, image light is provided by an image source, such as a microdisplay, to a partially reflecting mirror. In step 920, the partially reflecting mirror reflects a first portion of the image light while transmitting a second portion of image light. In step 930, a first portion of scene light is transmitted through a light control element. A
second portion of the scene light is transmitted through the partially reflecting mirror while a third portion of the scene light is reflected from the partially reflecting mirror in step 940.
In step 950 the first portion of image light and the second portion of scene light are combined to provide a combined image to the user's eye wherein the combined image is comprised of the displayed image from the image source overlaid on a see-through view of the external scene in front of the user. In step 960, the light control element blocks escaping light from the second portion of the image light and the third portion of the scene light to thereby reduce eyeglow. Wherein the percentage of light in the first portion of scene light that is transmitted through the light control element is larger than the percentage of escaping light from the second portion of image light and the third portion of scene light that is not blocked by the light control element.

[0047] The partially reflecting mirror included in the apparatus can have a range of reflectivity from 20% to 80%. Wherein the lower levels of reflectivity provide for more scene light to be presented to the user's eye so that the see-through view is brighter but, higher levels of image light will escape so that power usage for the image source will be increased to provide a displayed image with a given level of brightness. In contrast, higher levels of reflectivity provide for less scene light to be presented to the user's eye so that the see-through view is dimmer and lower levels of image light will escape, so that power usage for the image source will be reduced to provide a displayed image with a given level of brightness.

[0048] By using polarization based methods to reduce eyeglow, the efficiency of the light usage is increased. Linear polarizers typically block 99.9% or greater of one linear polarization state while allowing 99.9% of the other linear polarization state to pass through. Unpolarized light is comprised of a mixture of the two linear polarization states so that 50% of the unpolarized light is blocked and 50%
passes through the linear polarizer. Purely absorbing filters or purely reflecting filters cannot block a higher percentage of light than they pass under any circumstances. In the embodiments, the polarization states of the various portions of the image light and the scene light are controlled in the see-through display assembly and the light control element such that a high percentage of scene light is allowed to pass into the see-through display assembly while a higher percentage of escaping light is blocked so that a bright see-through view is presented to the user and eyeglow is reduced.
Considering that in some cases, the image light or the scene light may take on some elliptical polarization, it is reasonable to expect that the light control element blocks greater than 90% of the escaping light while allowing greater than 30% of the scene light to be transmitted.

[0049] The polarizing beam splitter in the embodiments discussed herein can be of several different types. While the examples shown in FIGS. 4, 6 and 8 show wiregrid plates or wiregrid films applied to support plates as the polarizing beam splitters, MacNeil prism type polarizing beam splitters can also be used.

[0050] In yet another embodiment, light absorbing structures are included on one or more of the edges of the frame 105 to absorb light that is reflected or scattered from the user's face. Where the light absorbing structures can include black areas or textured areas. The light absorbing structures can also be flexible to conform to the user's face.

[0051] Table of numerals for figures 100 see-through head 452 optical axis 653 quarter wave film mounted display device 102 clear areas of 460 folding 654 linear polarize lenses mirror 105 frames 465 scene light 690 combined image light 110 lenses 470 image light 700 light control element 115 display areas 480 light control 740 support layer element 120 camera 500 see-through 800 glasses cross-section display assembly 125 electronics 520 image source 805 glasses frame 127 peripheral 530 back surface 885 supporting member electronics of waveguide 130 arms 540 partially 887 supporting member reflective mirror 190 externally 550 optical axis 910 step of providing image observable image light to the partial mirror 400 see-through 555 waveguide 920 step of reflecting and display assembly transmitting portions of image light 410 user's eye 560 corrective 930 step of transmitting scene element light through the light control element 420 beam splitter layer 565 scene light 940 step of transmitting and reflecting portions of scene light 430 quarter wave film 570 image light 950 step of combining image light and scene light to provide a combined image to the user 440 partially reflective 580 light control 960 step of using the light mirror element control element to block escaping light 450 optical axis 652 controllable darkening layer

[0052] The present disclosure has been very detailed with particular reference to certain embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A see-through head mounted display apparatus with reduced eyeglow, comprising:
a see-through display assembly including an image source and a partially reflecting mirror that reflects and transmits respective portions of image light from the image source and scene light from a see-through view of an external environment, so that a combined image comprised of portions of the reflected image light and the transmitted scene light is provided to a user's eye; and a light control element that blocks escaping light comprised of the transmitted portion of image light and the reflected portion of scene light, while permitting a portion of incoming scene light to be transmitted from the external environment to the see-through display assembly, wherein the transmitted percentage of incoming scene light is greater than the percentage of escaping light that is not blocked.

2. The apparatus of claim 1 wherein the light control element blocks greater than 90% of the escaping light while allowing greater than 30% of the scene light to be transmitted.

3. The apparatus of claim 1 wherein the light control element comprises a linear polarizer.

4. The apparatus of claim 3 wherein the light control element further comprises a first quarter wave film.

5. The apparatus of claim 1 wherein the partially reflecting mirror is a spherical or aspheric mirror.

6. The apparatus of claim 3 wherein the see-through display assembly further comprises a partially reflecting mirror beam splitter layer and the image source provides linearly polarized image light.

7. The apparatus of claim 4 wherein the see-through display assembly further comprises a polarizing beam splitter and a second quarter wave film disposed between the polarizing beam splitter and the partially reflecting mirror.

8. The apparatus of claim 7 wherein the image source provides linearly polarized image light that is aligned to reflect from the polarizing beam splitter prior to passing through the second quarter wave film, and the linear polarizer in the light control element is aligned to transmit light through the polarizing beam splitter after passing through the first and second quarter wave films.

9. The apparatus of claim 8 wherein the polarizing beam splitter is a MacNeil beam splitter.

10. The apparatus of claim 8 wherein the polarizing beam splitter is a wire grid polarizer.

11. The apparatus of claim 3 wherein the light control element further comprises a controllable darkening layer.

12. The apparatus of claim 11 wherein the controllable darkening layer is comprised of two or more separately controllable areas.

13. The apparatus of claim 3 wherein the light control element further comprises a photochromic layer.

14. The apparatus of claim 1 wherein the see-through display assembly further comprises light absorbing structures on at least one edge of the see-through display assembly.

15. The apparatus of claim 1 wherein the image source is a projector.

16. The apparatus of claim 15 wherein the projector has a folded optical path.

17. The apparatus of claim 3 wherein the see-through display assembly further comprises a waveguide and the image source provides linearly polarized image light.

18. The apparatus of claim 17 wherein the image light is reflected multiple times from different areas of the partially reflecting mirror.

19. The apparatus of claim 1 wherein the light control element is a separately replaceable element.

20. The apparatus of claim 1 wherein the light control element, the partially reflective mirror and the user's eye are located along a common optical axis.

21. The apparatus of claim 1 wherein the escaping light further comprises light reflected or scattered from the user.

22. The method of claim 1 wherein the light control element includes a support layer with impact resistance, ballistic protection or laser protection.

23. A method for viewing an image with reduced eyeglow on a see-through head mounted display having a front and back, the method comprising:
providing image light to a partially reflecting mirror from an image displayed on an image source;
reflecting a first portion of the image light from the partially reflecting mirror while transmitting a second portion of the image light through the partially reflecting mirror;
transmitting a first portion of scene light from the external environment through a light control element at the front of the see-through head mounted display;
transmitting a second portion of the scene light through the partially reflecting mirror while reflecting a third portion of the scene light from the partially reflecting mirror;
combining the first portion of the image light with the second portion of the scene light to provide a combined image to a viewer's eye at the back of the see-through head mounted display comprised of the image displayed on the image source overlaid on a view of the external environment; and using the light control element to block the transmitted second portion of the image light and the reflected third portion of the scene light to reduce eyeglow.

24. The method of claim 23 further comprising using the light control element to block greater than 90% of the transmitted second portion of the image light and the reflected third portion of the scene light, while allowing greater than 30% of the incoming scene light to be transmitted.

25. The method of claim 23 further comprising using the light control element to block light from the combined image that is reflected from the viewer.

26. The method of claim 23 further comprising providing a linear polarizer in the light control element to block portions of image light and scene light while transmitting portions of scene light.

27. The method of claim 26 further comprising providing an image source that provides linearly polarized image light.

28. The method of claim 27 further comprising providing a first quarter wave film in the light control element; and using the first quarter wave film to convert linearly polarized scene light to circularly polarized scene light.

29. The method of claim 27 further comprising aligning the light control element, the partially reflective mirror and the viewer's eye along a common optical axis.

30. The method of claim 29 further comprising providing a beam splitter layer for reflecting and redirecting a portion of the polarized image light along the common optical axis.

31. The method of claim 30 wherein the beam splitter layer is a polarizing beam splitter layer and further comprising disposing a second quarter wave film between the polarizing beam splitter layer and the partially reflecting mirror; and using the first and second quarter wave films to reverse the polarization state of the first and second portions of the image light and reverse the polarization state of the first, second and third portions of the scene light.

32. The method of claim 31 further comprising aligning the polarized image light and the linear polarizer in the light control element so that the first portion of the polarized image light with reversed polarization state and the second portion of the scene light with reversed polarization state are transmitted through the polarizing beam splitter layer.

33. The method of claim 23 further comprising providing in the light control element a controllable darkening layer to partially block the first portion of scene light thereby reducing scene light in a portion of the combined image.

34. The method of claim 23 further comprising providing in the light control element a photochromic layer to partially block the first portion of scene light thereby reducing scene light in the combined image.

35. The method of claim 23 wherein the step of providing image light to a partially reflecting mirror includes using a waveguide.

36. The method of claim 23 further comprising using an absorbing structure to absorb light that is reflected or scattered from the user.