Patent Description:
A look-through display <NUM> is illustrated in <FIG>. Look-through display <NUM> comprises a waveguide <NUM> and a semi-reflective element <NUM>. Collimated light may be input into waveguide <NUM>, and is output towards semi-reflective element <NUM>. Semi-reflective element <NUM> reflects the collimated light back through the waveguide <NUM> towards an eye of a user and also allows light to pass from the outside towards the user's eye. The light reflected by the semi-reflective element remains substantially collimated, and so the user perceives the image to be focussed substantially at infinity. In some examples this may reduce the user experience, for example causing discomfort or headaches to the user, especially if the user desires to focus on a real object in their view and also observe the displayed symbology/imagery, that may be associated and/or overlaid with the real object.

<FIG> illustrates an optical system <NUM> according to some examples. Optical system comprises an expansion waveguide <NUM> and an optically powered element <NUM> comprising holographic components to provide the optical power. Light may be input into expansion waveguide <NUM>, and is expanded in at least one dimension, such that the size of the exit pupil increases in at least one dimension. Output element <NUM> interacts with the light and causes the light to be output towards optically powered element <NUM>. Light is output collimated, or substantially collimated. Optically powered element <NUM> adds an angular offset to the collimated light, causing the collimated light to diverge and form a virtual image plane <NUM>. This enables the user to perceive the image displayed by the optical system <NUM> to be located a certain distance behind the waveguide defined by the virtual image plane <NUM>. This may reduce eye strain and headaches for some users, leading to a better user experience.

In some examples the optical element <NUM> may be transparent or semi transparent, allowing a user to look through the optically powered element <NUM> and observe objects beyond the optical element <NUM>. In some examples where the optical element <NUM> is not transparent, the optical geometry of the optical system may allow the user to still see imagery overlaid with real objects in the user's field of view. These are explained in more detail with reference to <FIG> and <FIG>.

In some example the optically powered element <NUM> may comprise a thin positive meniscus (convex-concave) shaped element. The convex side facing the user may be coated with a partially reflective coating (beam splitter coating) which would reflect light emitted from the waveguide back towards the user whilst causing the collimated light emitted from the waveguide to diverge forming a virtual image plane <NUM>. The convex side facing away from the user may be shaped in order to minimise any aberrations of the outside world view when viewed through the optically powered element <NUM>.

In some examples the optical system <NUM> may be configured to compensate for the effect of the optical system on external light passing through the waveguide <NUM> and/or optically powered element <NUM> such that the outside scenery is not distorted. In some examples compensation may comprise an adaptation and/or addition to the optically powered element <NUM>. In some examples the compensation may comprise a separate optical element.

In some examples collimated light may be input into waveguide <NUM>. In some examples uncollimated light may be input into the waveguide <NUM> and the light may be collimated by a component of the waveguide <NUM>.

In some examples there may be an gap, such as an air gap, between the optically powered element <NUM> and the waveguide. In some examples the optically powered element may be coupled to the waveguide <NUM>.

In some examples the optically powered element <NUM> may comprise a holographic component which gives the optically powered element <NUM> optical power. This may allow the optical power to be varied by changing the phase of light input to the optically powered element <NUM>.

In some examples the holographic component may be static, such that it does not vary. In some examples the holographic component may be dynamic, such that it's properties can be varied. In some examples the dynamic holographic component may comprise an addressable and switchable reflective screen, such as liquid crystal display. This may allow the optical power to be varied by changing the phase of light and/or by changing the properties of the holographic component.

<FIG> illustrates an adjustable optical system <NUM> according to some examples. Adjustable optical system <NUM> may be substantially similar to optical system <NUM> described in relation to <FIG>. Adjustable optical system <NUM> comprises an expansion waveguide <NUM> and an adjustable optically powered element <NUM>. The expansion waveguide <NUM> may be substantially similar to the expansion waveguide <NUM> described in relation to <FIG>.

Adjustable optical system may be controlled to alter the optical power of the system. In some examples the optically powered element <NUM> may be controlled to vary the optical power. In some examples the optical power may be varied into at least two states. In a first state the adjustable optically powered element <NUM> has a first optical power, leading to a virtual image plane 340a at a first distance from the user. In a second state the adjustable optically powered element <NUM> has a second optical power, different from the first optical power, leading to a virtual image plane 340b at a second distance from the user. The difference in optical power of the first state and second state cause a difference in position <NUM> of the virtual planes 340a, 340b.

In some examples the adjustable optically powered element <NUM> may adjust it's optical power based on tracking information of the user's eyes, such as a focus or gaze direction of the eyes.

In some examples the adjustable optically powered element <NUM> may be continuously adjustable between two points. In some examples the adjustable optically powered element <NUM> may be discretely variable, such that the adjustable optically powered element <NUM> may be set to a finite number of optical powers between two points.

In some examples the adjustable optically powered element <NUM> may be varied in optical power by adjusting the curvature of the adjustable optically powered element <NUM>. Adjusting the curvature may result in the image plane changing, but the focal point may fall on the same axis, i.e. the focal points may all be located on a line that is perpendicular to the output surface of the waveguide.

In some examples the adjustable optically powered element <NUM> may be varied in optical power by adjusting the shape of the adjustable optically powered element <NUM>. Adjusting the shape may result in the image plane changing, and the focal point may fall on a different axis, i.e. the focal points are not all located on a line that is perpendicular to the output surface of the waveguide.

In some examples the adjustable optically powered element <NUM> may be varied in optical power between having no optical power (i.e. substantially flat with focus at infinity) and any other focal point.

In some examples the adjustable optically powered element <NUM> may comprise a microelectromechanical system (MEMS), and/or a piezoelectric device. In some examples the adjustable optically powered element <NUM> may comprise a electronically active element such as a reflective liquid crystal. In some examples the adjustable optically powered element <NUM> may comprise a, diffractive, pneumatic, and/or hydraulic device.

In some examples the optically powered element <NUM> may comprise a holographic lens of fixed optical power. This may allow the lens to be tuned for wavelength, therefore able to maintain high transmission compared to a traditional silver mirror and able to be colour selective. The fixed holographic lens of fixed optical power may additionally or alternatively be tuned for angle. This may allow the lens to be angularly selective i.e. reflect incoming angles from a known field of view but transmit all other light.

The holographic lens of fixed optical power may be substantially flat and/or thin - i.e. formed from a holographic layer between two glass or plastic plates, in comparison to a traditional lens or mirror arrangement where the element is typically curved and/or potentially thick. If the holographic lens is then placed in line with the eye, being a thin and/or flat element mitigates any distortion being imparted on the real world. In some examples where the lens element is placed in line with the waveguide, using a thin/flat holographic lens could also be integrated as a protective cover for the waveguide as well.

In some examples the optically powered element <NUM> may comprise a holographic lens of variable function, such as variable power or reflectivity. A holographic lens of variable function may offer all the same features as the holographic lens of fixed optical power. The optical power may be varied either through electrical manipulation or physical manipulation of the holographic medium. The reflectivity may be varied to manipulate reflection intensity or the ability to "switch off" the hologram (and hence reflection) entirely. The holographic lens of variable function may be substantially flat and/or thin similar to the holographic lens of fixed optical power.

Holographic lenses may also be stacked together to form various functions. For example you could stack a holographic lenses for green and red light may be stacked, wherein they have different optical powers or reflectivity.

In some example the adjustable optically powered element <NUM> may comprise a thin positive meniscus (convex-concave) shaped element. The convex side facing the user may be coated with a partially reflective coating (beam splitter coating) which would reflect light emitted from the waveguide back towards the user whilst causing the collimated light emitted from the waveguide to diverge forming a virtual image plane <NUM>. The convex side facing away from the user may be shaped in order to minimise any aberrations of the outside world view when viewed through the adjustable optically powered element <NUM>.

<FIG> illustrates a folded optical system <NUM> according to some examples. The folded optical system <NUM> may be substantially similar to the optical system <NUM> described in relation to <FIG> and the adjustable optical system <NUM> described in relation to <FIG>. Folded optical system <NUM> comprises a waveguide <NUM>, an optically powered element <NUM>, and a combiner element <NUM>.

Waveguide <NUM> receives light, and outputs collimated light towards optically powered element <NUM>. Optically powered element <NUM> adds an angular offset to the reflected light and reflects it through waveguide <NUM> to combiner <NUM>.

Combiner <NUM> is at least semi-transparent such that the user is able to observe outside scenery through combiner <NUM>. The combiner reflects light from the waveguide <NUM> towards the eye of the user, such that the image plane <NUM> appears to be behind the combiner <NUM>.

The optically powered element <NUM> may be opaque, as there is no reason why the optically powered element <NUM> is required to be looked through. For similar reasons, the optically powered element <NUM> may also be highly reflective.

Folded optical system <NUM> may be used in head up displays (HUD) or head down displays, or any other suitable system.

<FIG> illustrates an offset optical system <NUM>. Offset optical system <NUM> may be substantially similar to the optical system <NUM> described in relation to <FIG>, the adjustable optical system <NUM> described in relation to <FIG>, and the folded optical system <NUM> described in relation to <FIG>.

Offset optical system <NUM> comprises an offset waveguide <NUM> and an offset optically powered element <NUM>. Offset waveguide receives offset input light <NUM>, which is expanded in at least one dimension and propagates down offset waveguide <NUM>. Due to the presence of element <NUM> the light is output from the offset waveguide <NUM>. The type of the offset waveguide <NUM> may lead to light being emitted on both sides of the offset waveguide <NUM>, as illustrated in <FIG>. User light <NUM> emitted towards the offset optically powered element <NUM> is reflected by offset optically powered element <NUM> and an angular offset added such that the light diverges and forms a virtual image plane <NUM>. The light then passes through the waveguide again such that the user observes the image to be formed at the virtual plane <NUM>. Non-user light <NUM> is emitted away from the user's eye and away from the offset optically powered element <NUM> such that it is not received by the user. This reduces the chance of a double image being observed by the user.

The offset optically powered element <NUM> may be designed, in combination with the offset waveguide <NUM> to ensure that light received from the offset optically powered element <NUM> appear to be focused at virtual image plane <NUM>.

In some example the offset optically powered element <NUM> may comprise a thin positive meniscus (convex-concave) shaped element. The convex side facing the user may be coated with a partially reflective coating (beam splitter coating) which would reflect light emitted from the waveguide back towards the user whilst causing the collimated light emitted from the waveguide to diverge forming a virtual image plane <NUM>. The convex side facing away from the user may be shaped in order to minimise any aberrations of the outside world view when viewed through the offset optically powered element <NUM>.

<FIG> illustrates a birdbath style optical system <NUM> according to some examples, where the light does not pass back through the waveguide. Birdbath style optical system <NUM> comprises a birdbath waveguide <NUM>, a semi-reflective mirror <NUM>, and a birdbath optically powered element <NUM>. The birdbath waveguide is configured to receive light and output collimated light towards the semi-reflective mirror <NUM>. The semi-reflective mirror <NUM> allows all or substantially all of light to pass from the birdbath waveguide <NUM> towards the birdbath optically powered element <NUM>. Birdbath optically powered element <NUM> imparts an angular offset onto the light such that it diverges and forms a virtual image plane <NUM>. The light is reflected from birdbath optically powered element towards the semi-reflective mirror <NUM>. Semi-reflective mirror <NUM> reflects the light from the birdbath optically powered element <NUM> towards the user. The arrangement of <FIG> allows for at least one of the birdbath waveguide <NUM> and birdbath optically powered element <NUM> to be opaque, or substantially opaque.

The semi-reflective mirror may appear transparent to visible light or substantially transparent to visible light from the viewing angle of the user.

The figures merely illustrate a single colour of light in the optical systems. However, this is for convenience and ease of understanding the drawings, and that any suitable number of colours may be appropriate depending upon the usage of the optical systems.

In some examples the optically powered element may be flat or substantially flat.

Claim 1:
An optical system to present an image to an eye of a user, the system comprising:
a waveguide (<NUM>) configured to output collimated light towards an optically powered element (<NUM>) comprising at least one holographic component (<NUM>) to generate optical power;
the optically powered element configured to receive the output collimated light from the waveguide and direct the received light towards the eye of the user and impart an angular offset on the directed light such that the directed light forms a virtual image plane (<NUM>),
wherein the optically powered element is configured to receive the output collimated light from the waveguide and direct the received light towards the eye of the user through the waveguide,
wherein the optically powered element is tilted with respect to an optical axis of the waveguide, and
wherein the waveguide is configured to emit a portion (<NUM>) of received light away from the eye of the user from an opposite side of the waveguide from which the collimated light is emitted towards the optically powered element, and light reflected from the tilted optically powered element is emitted towards the eye of a user through the waveguide.