Patent Description:
Head-up displays, HUD, are often used in vehicles, such as airborne vehicles and land-borne vehicles, for presenting information to an operator of the vehicle in such a way that the operator simultaneously is able to see the surrounding of the vehicle through a window. The information is preferably also shown at the same (virtual) image distance as the viewing distance to the surroundings. Thus no or only very little eye moving is needed for between looking at the presented information and looking at the surrounding. The operator can also fast detect changes in the surrounding when looking at presented information, or vice versa.

HUD are, however, often quite space-consuming. This can be understood as follows. The presented information reaches the eye(s) of a user of the HUD via light beams. These light beams originate from an image source and have to pass optical components on the way from the image source to the eye(s). Even if there were usable transparent image sources, these could usually not be used directly, since the image also preferably has to appear to be at a reasonably far distance, comparable to the viewing distance to the surrounding outside world. The light beams from the image source thus have to pass the optical components for focussing and/or defocussing of the image, magnification and/or demagnification of the image, changing of the direction of the light beams, or the like. There is thus usually quite some space needed in between the optical components since the distance between the components is determined by the focal length of lenses, and/or the focal length of convex or concave mirrors, or any other optical parameters. Also, especially for an off axis solution, where the optical combiner is not flat and the combiner is tilted relative to the optical axis so that the reflected light is directed away from the incident light, a large number of optical surfaces are required to adequately correct for the optical aberrations. This not only gives a larger space envelope, but also a large weight.

On the other hand, more and more devices are added to vehicles. Since the total size of the vehicle usually should not increase, there is thus a need to build more compact HUDs which require less space.

Reference is made to <CIT> which discloses a head-up display comprising an image source, an optical element having a free-form surface, a flat lens and a combiner.

SUMMARY OF THE INVENTION The invention is defined by independent claim <NUM>, with preferred embodiments set out in the dependent claims.

It is an objective of the present disclosure to present a more compact design for a HUD.

It is an objective of the present disclosure to present an alternative design for a HUD.

A solution to the objectives is partially allowed by the development of new manufacturing technologies, e.g. for free-form surfaces.

At least some of the objectives are achieved by a head-up-display, HUD. The HUD is arranged to project an image to at least one eye of a user of the HUD. The HUD comprises an image source. The HUD further comprises an optical component. The optical component comprises at least one free-form surface. The optical component is arranged in an optical path between the image source and the intended position of said at least one eye of the user of the HUD. The HUD further comprises a flat lens comprising a structured lens pattern on at least one of its surfaces. The structured lens pattern has a feature size in the order of <NUM> up to <NUM>. The flat lens is arranged in the optical path between the image source and the intended position of said at least one eye of the user of the HUD. The HUD further comprises a combiner. At least one surface of the combiner is a free-form surface. The combiner is arranged in the optical path between the optical component and the intended position of said at least one eye of the user of the HUD.

This has the advantage that a compact design is achieved. The flat lens and the free-form surfaces allow aberrating and/or blurring the image in unconventional ways and to compensate this aberration and/or blurring again so that a "right" image is projected at the eye of the observer. The free-form surfaces and the flat lens add additional degrees of freedom to the design of a HUD. These additional degrees of freedom can then be used to skip further lenses, mirrors, prisms, and/or other optical components. All this allows reducing space constraints of the HUD.

According to the invention, the image source is arranged to provide the image to be projected via a curved image plane, or generally via a non-planar image plane. This has the advantage that an even more compact design can be achieved.

In one embodiment of the HUD the image source is arranged to provide the image via the curved image plane in the optical path before the optical component and the flat lens. This allows having the curved image plane close to the image source, thus allowing a compact design of the light source and its surrounding.

In one embodiment the HUD further comprises a fibreoptic faceplate. The curved image plane is provided via the faceplate. This allows a compact solution for providing the curved image plane. The number of components for achieving a curved image plane is reduced.

In one embodiment the image source comprises a curved display. The curved image plane is provided via the curved display. This requires no extra components for achieving a curved image plane, thus allowing having an even more compact design with few optical surfaces/components.

In one embodiment the flat lens is arranged in the optical path between the image source and the optical component. This allows using a smaller flat lens, thus reducing weight.

In one embodiment the flat lens is arranged in the optical path between the optical component and the combiner. This allows for a better possibility to change the flat lens and/or to inspect the flat lens for damages. The flat lens can also partly function as a beam direction turning device. This can also make the design more compact.

In one embodiment the flat lens is attached to the optical component. This allows for a robust design, especially when the HUD is subjected to vibrations.

In one embodiment the flat lens is arranged at a distance from the optical component. This is advantageous in case the flat lens and the optical component have different coefficients of thermal expansion.

In one embodiment the flat lens is curved. This allows for more design options, for example integrating the flat lens with the optical component.

In one embodiment a smooth surface of the flat lens is oriented towards the optical component. This allows an easy attaching.

In one embodiment a smooth surface of the flat lens is oriented away from the optical component. This allows protecting the structured lens pattern from dust and other deposits. This also protects the structured lens pattern from scratching or the like.

In one embodiment no light beam redirecting optical components such as lenses, mirrors, and/or prisms are arranged in the optical path between the combiner and the intended position of said at least one eye of the observer. By keeping down the number of elements between the eye of the observer and the surrounding the HUD will create a less disturbing influence to a user of the HUD.

In one embodiment the HUD does not comprise any further light beam redirecting optical components. This keeps space requirements low. Further, this increases stable operation of the HUD as each additional component would potentially add a risk for misalignment.

In one embodiment the feature size has a height which is in the order of <NUM> up to <NUM>. This reduces the risk for "shadowed" areas in the flat lens.

In one embodiment the HUD is arranged to be used in an airborne vehicle, such as an airplane. Especially for airplanes space and weight savings due to a compact design will easily pay off by saved operational and constructional costs.

In one embodiment the flat lens and the optical component are integrated into a single component made of the same material.

At least some of the objectives are achieved by an airborne vehicle, such as an airplane, comprising a HUD according to the present disclosure. Especially for airplanes space and weight savings due to a compact design of the HUD will easily pay off by saved operational and constructional costs.

For a more detailed understanding of the present invention and its objects and advantages, reference is made to the following detailed description which should be read together with the accompanying drawings. Same reference numbers refer to same components in the different figures. In the following,.

Here, and in the whole document, the term "free-form" refers to a surface which is neither plane nor spherical.

Here, and in the whole documents, the term "oriented" refers to an orientation in relation to a light path. Thus, an orientation of one object in relation to another object does not necessarily relate to a direct physical orientation between these objects, but rather to an orientation considering a light path is followed. However, a direct physical orientation and an orientation in relation to the light path can coincide as will become obvious from the drawings.

<FIG> schematically depicts a vehicle <NUM> according to the present disclosure. In the shown example the vehicle <NUM> is an airborne vehicle, more specifically an airplane. The airplane can be a passenger plane or a military plane. The airplane can be of any size, such as a one-, or two-seated airplane, or an airplane for many passengers and/or freight transport. The airborne vehicle can, however, be any other kind of airborne vehicle as well, such as helicopters, dirigibles, or the like. The vehicle <NUM> comprises a head-up display, HUD, <NUM> which will be described in more detail in relation to <FIG>. Although the vehicle <NUM> is depicted as an airborne vehicle, the vehicle can in principle be any other kind of vehicle as well, such as land-borne or sea-borne vehicles.

<FIG> schematically depict cross-sections of different embodiments of a HUD <NUM> according to the present disclosure. Throughout the figures, same reference numbers describe the same elements. Not every element is described in detail in relation to every embodiment. Instead, it can in general be assumed that elements without further description in one embodiment possess the same functions and properties as have been described in relation to a corresponding previous embodiment. In all embodiments an eye <NUM> of an observer is depicted. The HUD <NUM> is arranged to provide an image to the eye <NUM> of the observer when the eye <NUM> of the observer is situated at a pre-determined position. Said pre-determined position does not have to be a single pre-determined position but can in principle be a certain three-dimensional space in which the eye of the observer should be placed. In one example the HUD <NUM> is arranged to provide said image to one eye of the observer. In one example the HUD <NUM> is arranged to provide said image to both eyes of the observer. In the following the description refers for simplicity to one eye, but it should be understood that this equally applies to the case where the HUD <NUM> is used for two eyes.

The eye <NUM> of the observer has a line of sight <NUM>. When being in the pre-determined position and looking at the line of sight <NUM>, the eye <NUM> of the observer will be able to see a surrounding, such as a surrounding of the vehicle. This is achieved by light from the surrounding reaching the eye <NUM> of the observer.

The image which is provided by the HUD <NUM> is in a preferred example directed to the eye <NUM> of the observer, where it might be projected on the retina of the eye.

It should also be understood that the HUD <NUM> in general can comprise further elements as those depicted in the figures, such as elements for holding the different components at a given position, cables for data and/or power supply, or the like. However, components which do not affect the appearance of the image which is provided by the HUD have been removed from the <FIG>.

The HUD <NUM> comprises a combiner <NUM>. The combiner <NUM> comprises a first surface <NUM>. The first surface <NUM> is oriented towards the eye <NUM> of the observer. The combiner <NUM> comprises a second surface <NUM>. The second surface <NUM> is oriented away from the eye <NUM> of the observer. The combiner is preferably semi-transparent. Light from the surrounding can reach the eye <NUM> of the observer via first passing the second surface <NUM> of the combiner <NUM> and then the first surface <NUM> of the combiner. At least one of the first and the second surfaces <NUM>, <NUM> of the combiner <NUM> are free-form surfaces. In other words, that surface is neither plane nor spherical. Instead, the form of the surface can be described by a polynomial function or equation, as long as this polynomial function or equation does not describe a plane or spherical surface, or can be described by any other function or equation. The combiner is arranged in the optical path between an optical component <NUM> and the intended position of said at least one eye of the user of the HUD.

<FIG> schematically depicts a cross-section of a first embodiment of the HUD <NUM>. The HUD comprises an image source <NUM>. The image source <NUM> comprises a first surface <NUM>. The image source is arranged to emit light via the first surface <NUM>. The image source <NUM> can be a display arrangement. The display arrangement can comprise a liquid crystal display, LCD, and/or a display based on light emitting diodes, LED. Said display based on LED can be a display based on organic LED, OLED. Even any other display type could be used. The image source <NUM> can be a projector arrangement.

The HUD <NUM> can comprise a fibreoptic faceplate <NUM>. The faceplate <NUM> comprises a first surface <NUM>. The first surface is preferably oriented towards the image source <NUM>. The faceplate comprises a second surface <NUM>. The second surface <NUM> is preferably oriented away from the image source <NUM>. In case the image source <NUM> comprises a projector arrangement, the projector arrangement can be arranged to project the image on the first surface <NUM> of the faceplate <NUM>. In one example there is a distance between the first surface <NUM> of the image source <NUM> and the first surface <NUM> of the faceplate <NUM>. Such a distance is depicted in the embodiment of <FIG>. Said distance is especially preferred in case the image source <NUM> comprises a projector arrangement. However, a distance can also be present in case no projector arrangement is present.

The second surface <NUM> of the faceplate <NUM> can be a curved surface. This allows providing the image from the image source <NUM> via a curved image plane. In this case the curved image plane corresponds preferably to the curved second surface <NUM> of the faceplate. In one example the first surface <NUM> of the faceplate <NUM> is plane surface and the image "enters" the faceplate in a plane image via the first surface <NUM> of the faceplate <NUM>.

The HUD further comprises an optical component <NUM>. The optical component <NUM> comprises a first surface <NUM>. The first surface is oriented towards the image source <NUM>. The optical component comprises a second surface <NUM>. The second surface <NUM> is oriented towards the eye of an observer. At least one of the first and the second surface <NUM>, <NUM> of the optical component <NUM> is a free-form surface. The optical component <NUM> is arranged to affect a change of direction of propagation for light beams entering the optical component from the image source <NUM>. Said change of direction is preferably performed for basically any light beam entering the optical component from the image source <NUM>. The optical component <NUM> is arranged in the optical path between the image source and the intended position of the eye of the user of the HUD. The optical component preferably has an index of refraction which differs from the index of refraction of air and/or vacuum. The optical component <NUM> can be made out of glass and/or plastic. The optical component <NUM> is preferably transparent. The form of the optical component is further described in relation to <FIG> and Fig. 4a-c.

The HUD <NUM> further comprises a flat lens <NUM>. The flat lens <NUM> comprises a first surface <NUM>. Said first surface <NUM> is preferably an even, i.e. a smooth surface. The flat lens <NUM> comprises a second surface <NUM>. Said second surface preferably comprises a structured lens pattern. The structured lens pattern has preferably a feature size in the order of <NUM> up to <NUM>. In one example said feature size is in the order of <NUM> up to <NUM>. In one example said feature size is in the order of <NUM> up to <NUM>. The structured lens pattern is further explained in relation to <FIG>. The term "flat" does relate to the fact that the average distance between the first and the second surface <NUM>, <NUM> of the flat lens <NUM> does not vary substantially throughout the extension of the first and second surface <NUM>, <NUM>, i.e., for example, that the average distance between the first and the second surface <NUM>, <NUM> in the middle of the lens is not significantly different from the average distance between the first and the second surface <NUM>, <NUM> in the side regions of the lens. In this relation the average distance should be taken over the extension of one or a few features when seeing them in a cross section such as in <FIG>. Thus the term flat does neither demand that the first and second surface <NUM>, <NUM> should be a straight line, nor that the first and second surface <NUM>, <NUM> should be even, i.e. completely plane. Instead the term flat relates to the fact that the lens is "flattened" in relation to a conventional lens. An example of a "flattened" lens which is well-known in the art is a Fresnel lens. The flat lens <NUM> is arranged in the optical path between the image source <NUM> and the intended position of the eye <NUM> of the user of the HUD. In the shown example, the flat lens <NUM> is arranged in the optical path between the optical component <NUM> and the combiner <NUM>.

In the example of <FIG> the first surface <NUM> of the flat lens <NUM> is adjacent to the second surface <NUM> of the optical component <NUM>. The first surface <NUM> of the flat lens <NUM> can be fixedly attached to the second surface <NUM> of the optical component <NUM>. The first surface <NUM> of the flat lens <NUM> can also be integrated with the optical component <NUM> if the flat lens <NUM> and the optical component <NUM> are of the same material. Thus, they could be manufactured as one component, e.g. by moulding. This has the advantage that the internal relation between the optical component <NUM> and the flat lens <NUM> and thus the beam travelling between these components remains constant even under tough conditions, such as strong shakings of the HUD. In one example one or several intermediate layers are arranged between the optical component <NUM> and the flat lens <NUM>.

What has been described regarding the image source <NUM>, the faceplate <NUM>, the flat lens <NUM> and the optical component <NUM> in relation to the first embodiment applies equally to all other embodiments as long as not explicitly described or depicted differently in relation to these embodiments.

<FIG> schematically depicts a cross-section of a second embodiment of the HUD <NUM>. One difference between the first and the second embodiment is that the first surface <NUM> of the faceplate <NUM> is attached to the first surface <NUM> of the image source. This is advantageous in case the image source comprises a display. In that way a compact arrangement can be achieved as no air slit is needed between the image source <NUM> and the faceplate <NUM>. The light leaving a pixel of the display will then be emitted into a bunch of fibres in the faceplate. Different pixels will emit the light into different bunches of fibres. By this it will than appear as if the image which is emitted by the image source <NUM> is emitted by the faceplate <NUM> instead.

Instead of a direct attachment between faceplate <NUM> and image source <NUM>, one or several intermediate layers could be used in between the faceplate <NUM> and the image source <NUM>. These one or several layers are preferably quite thin, especially thin in comparison to the thickness of the faceplate <NUM>.

In the second embodiment, the flat lens <NUM> is not directly attached to the optical component <NUM>. Instead, an air slit, or a slit of any other, preferably non-solid, material is arranged between the optical component <NUM> and the flat lens <NUM>. This is especially advantageous in case the optical component <NUM> and the flat lens <NUM> have different coefficients of thermal expansion. Since, especially on airborne vehicles, quite large temperature changes can occur during short times the slit can prevent the occurrence of too high tensions between the flat lens <NUM> and the optical component <NUM>.

<FIG> depicts a third embodiment of the HUD according to the present disclosure. In this embodiment the flat lens <NUM> is situated in the optical path between the image source <NUM> and the optical component <NUM>. This has the advantage that the flat lens <NUM> can be made smaller compared to the first or second embodiment. This is due to the fact that the flat lens <NUM> does not need to extend to a length which approximately corresponds to the second surface <NUM> of the optical component <NUM>. In the shown embodiment the surface of the flat lens comprising the structured lens pattern is oriented towards the optical component <NUM>.

<FIG> depicts a fourth embodiment of the HUD according to the present disclosure. In this embodiment the second surface <NUM> of the optical component <NUM> is convex. This is in comparison to the previous embodiments wherein the second surface <NUM> of the optical component <NUM> could be seen as a straight line when seen in a cross-section. The flat lens <NUM> is arranged in the optical path between the image source <NUM> and the optical component <NUM>. In an alternative embodiment, the flat lens <NUM> is arranged on the second surface <NUM> of the optical component <NUM>. Thus the flat lens <NUM> can be curved.

<FIG> depicts a fifth embodiment of the HUD according to the present disclosure. In this embodiment the flat lens <NUM> is curved. The flat lens <NUM> is arranged at the first surface <NUM> of the optical component <NUM>. The flat lens <NUM> and the optical component <NUM> can be arranged as the same component. As an example, the flat lens can be machined directly on the first surface of the optical component. This has the advantage that one less component is needed.

In the shown example one side of the flat lens has the same form as the free-form side of the optical component.

In the shown example no faceplate <NUM> is present. In another example a small slit is provided between the image source <NUM> and the face plate <NUM>. This might be advantageous in case a direct attachment would risk produce too much tensions between these elements. Further, this might simplify replacing the image source in an easy way.

<FIG> a sixth embodiment of the HUD according to the present disclosure is depicted. In this example the second surface <NUM> of the optical material is a free-form surface. The flat lens <NUM> is situated in the optical path between the image source <NUM> and the optical component <NUM>. The flat lens <NUM> is situated in the optical path between the faceplate <NUM> and the optical component <NUM>. In an alternative embodiment the flat lens <NUM> is integrated with the faceplate. As an example the flat lens <NUM> is integrated with the second surface <NUM> of the faceplate <NUM>. In another example no faceplate <NUM> is present in the sixth embodiment.

In all embodiments examples of light beams 170a-170d are depicted to show in a schematic way how light beams emitted from the image source <NUM> can travel through the HUD to the eye of the observer. These examples of light beams 170a-170d are only for illustrative purposes for containing a better understanding of the relation and arrangement of the components of the HUD. In reality, the exact direction of light beams might differ from those depicted in <FIG>.

In one embodiment (not shown in the figures) no faceplate is needed. This can for example be achieved via having a curved first surface <NUM> of the image source <NUM>. A curved first surface <NUM> of the image source <NUM> allows directly providing the image to be projected via a curved image plane. A curved display surface with or without a faceplate <NUM> can be combined with any of the shown embodiments in <FIG>. The curved image plane does not necessarily need to be coupled to a physical element. In one example, the curved image plane is, so to say, "in the air".

In the depicted examples the flat lens <NUM> is oriented in such a way that the smooth surface is closer to another component, such as the optical material <NUM> or the faceplate <NUM>, than the surface with the structured lens pattern. In another example, the smooth surface of the flat lens <NUM> is oriented away from the optical material <NUM> and/or the faceplate <NUM>. As an example, in <FIG> the flat lens <NUM> could be arranged in such a way that the surface with the structured lens pattern is oriented towards the second surface <NUM> of the optical material <NUM>. This has the advantage that the surface with the structured lens pattern is better protected from damages and/or deposits.

The curved image plane is preferably provided in the optical path before the optical component <NUM> and before the flat lens <NUM>. In the foregoing some surfaces have been described as being free-form. However, in a further embodiment any other surface can be free-form as well as long as the requirements according to the independent claims still can be fulfilled.

The depicted six embodiments have been chosen to explain different advantages of different arrangements within the idea of the present disclosure. However, different aspects from the discussed embodiments can be easily combined to arrive at even further embodiments.

It should be emphasised that <FIG> is a cross section. It is by no means intended that the described elements just continue straight "in to the paper" or "out from the paper" when thinking of a three-dimensional representation. On the contrary, one or several of the discussed components can contain a complex surface structure when cutting them in a direction perpendicular to the cross section shown in <FIG>. This is for example further discussed in relation to <FIG>.

<FIG> schematically depict cross sections of different embodiments of the optical component <NUM>. The cross sections can be in the same direction as the cross sections in <FIG>. In all shown embodiments the first surface <NUM> of the optical component is a free-form surface. In the first embodiment depicted in <FIG> the second surface <NUM> of the optical component is an even surface. In the second embodiment depicted in <FIG> the second surface <NUM> of the optical component is a spherical convex surface. In the third embodiment depicted in Fig. 3c the second surface <NUM> of the optical component is a spherical concave surface. In the fourth embodiment depicted in <FIG> the second surface <NUM> of the optical component is a free-form surface. The examples of free-form surfaces in connection to this disclosure are only examples. In general, a free-form surface can look different from those depicted in the figures.

Producing an optical component with at least one free-form surface is generally harder than producing components with only plane and/or spherical surfaces. However, by using techniques such as computerised numerical control, CNC, diamond turning, stepper machines, application of floating polymers, hardening via UV-light and/or heat, and/or relating techniques, it is possible to produce the optical component <NUM>, the flat lens <NUM>, and/or other components with free-form optics.

<FIG> schematically depicts a perspective view of an embodiment of the optical component <NUM>. Two grids <NUM> are shown. The two grids are placed on opposite sides of the optical component. The lines of the grids <NUM> follow the surface structure of the optical component <NUM>. As can be seen, the optical component can have a complex structure even in the direction perpendicular to the cross-section shown in <FIG>. As can be seen from <FIG>the light originating from the image source can due to the optical component <NUM> be spread to a bigger area when arriving at the combiner. By having a non-trivial structure in the direction perpendicular to the cross-section shown in <FIG>, this effect of spreading the light beams over a bigger area can also be achieved in the direction perpendicular to the cross-section shown in <FIG>. This further reduces space requirements, especially in relation to the image source <NUM>, the optional faceplate <NUM> and the needed space between these elements and the optical component <NUM>.

<FIG> depicts several different examples of cross-sections of the flat lens <NUM>. In the shown examples the flat lens <NUM> is a Fresnel lens. In one example the flat lens <NUM> is a "flattened" cylindrical lens (lowest image, shown in perspective view). In one example (not shown) the flat lens <NUM> is a "flattened" elliptical lens. In one example the flat lens <NUM> is a "flattened" aspherical lens. This is depicted in the two middle images which show two different "flattened" aspherical lenses. At the image at the top a "flattened" spherical lens is depicted. The flat lens <NUM> can have different focal lengths in one cross-sectional plane and a perpendicular cross-sectional plane. For comparison, the "non-flattened" versions <NUM> of the lenses are depicted for three of the four images.

When arranged in the HUD, the flat lens <NUM> can be decentralised. In other words, the middle of the lens does not necessarily have to coincide with the middle of the light beams which are emitted from the light source <NUM> and transferred to the eye <NUM>. As an example, when looking at <FIG>, the flat lens <NUM> could be shifted to the left or to the right in relation to the optical component <NUM>.

One surface of the flat lens comprises a structured lens pattern <NUM>. The lens pattern <NUM> consists of different features <NUM>, <NUM>, <NUM>,. The features of the lens pattern <NUM> in general have a feature size in the order of <NUM> up to <NUM>. In one example all features of the lens pattern <NUM> have a height of the feature size in the order of <NUM> up to <NUM>. In one example basically all features of the lens pattern <NUM> have a height of the feature size in the order of <NUM> up to <NUM>. In one example most of the features of the lens pattern <NUM> have a height of the feature size in the order of <NUM> up to <NUM>. In one example the flat lens is a micro-pattern lens. In one example all or basically all heights of the features are smaller than <NUM>. In one example most of the heights of the features are smaller than <NUM>. In one example all or basically all heights of the features are smaller than <NUM>. In one example most of the heights of the features are smaller than <NUM>. In one example all or basically all heights of the features are bigger than <NUM>. In one example most heights of the features are bigger than <NUM>. What has been said regarding the height also applies regarding the width of the features. It should, however, be understood that at least at one point, for example in the centre of the flat lens, a width of more than <NUM> might be present. This can be seen in <FIG>.

Advantages of bigger feature sizes are that they can be produced more easily. However, depending on the design of the features, bigger feature sizes might produce shadowed areas. Smaller feature sizes might be harder to produce, but allow on the other side a lens with less thickness. Further, small feature sizes allow more optical aberration correction which can be used for achieving an even more compact design.

Some of the features of the flat lens <NUM> can have a diffractive effect to light beams. Thus the flat lens <NUM> can be a hybrid lens, i.e. a lens comprising refractive and diffractive properties. This allows for even more compact designs.

An advantage of a HUD according to the present disclosure is that no further optical components are needed. Especially, no further mirrors or lenses are needed for building up the HUD. Also, the elements of the HUD are not constrained to be positioned in such a way that further image planes are provided in the optical path. A distorted image can be emitted from the image source. The image only needs to look "right" in the eye <NUM> and not at any point before the eye. A drawback might be that the design process of the HUD becomes more complicated as it demands considerable computational power and/or advanced software to assure that a "right" image is seen by the eye. However, a considerably advantage is that a more compact arrangement will be achieved instead. The introduction of the free-form surfaces, the curved image plane after the image source and the flat lens allow using fewer surfaces to accomplish the required aberration corrections.

It should be understood that the HUD according to the present disclosure can comprise further components such as protection layers or the like. However, such additional components do in general not significantly redirect light beams originating from the image source and being intended for the eye of the observer. Thus said further components are in general no light beam redirecting optical components, such as lenses, prisms, mirrors, or the like.

Claim 1:
A head-up-display (<NUM>), HUD, arranged to project an image to at least one eye (<NUM>) of a user of the HUD, comprising:
- an image source (<NUM>);
- an optical component (<NUM>), comprising at least one free-form surface (<NUM>), wherein the optical component (<NUM>) is arranged in an optical path between the image source (<NUM>) and the intended position of said at least one eye (<NUM>) of the user of the HUD;
- a flat lens (<NUM>) comprising a structured lens pattern (<NUM>) on at least one of its surfaces (<NUM>), wherein the structured lens pattern (<NUM>) has features (<NUM>, <NUM>, <NUM>, ...) with heights in the order of <NUM> up to <NUM>, wherein the flat lens (<NUM>) is arranged in the optical path between the image source (<NUM>) and the intended position of said at least one eye (<NUM>) of the user of the HUD;
- a combiner (<NUM>), wherein at least one surface (<NUM>, <NUM>) of the combiner (<NUM>) is a free-form surface, and wherein the combiner (<NUM>) is arranged in the optical path between the optical component (<NUM>) and the intended position of said at least one eye (<NUM>) of the user of the HUD;
- wherein said image source (<NUM>) is arranged to provide the image to be projected via a curved image plane in the optical path before said optical component (<NUM>) and said flat lens (<NUM>).