Optical element with a fresnel structure, and display device with such an optical element

Provided is an optical element with a Fresnel structure with several Fresnel segments. Each Fresnel segment has an optically active facet, the shape of which is part of a predetermined surface. The predetermined surfaces of the optically active facets differ in terms of their curvature profile.

PRIORITY

This application claims the benefit of German Patent Application No. 102013214697.3, filed on Jul. 26, 2013, which is hereby incorporated herein by reference in its entirety.

FIELD

The present invention relates to an optical element with a Fresnel structure with several Fresnel segments, wherein each Fresnel segment has an optically active facet, the shape of which is part of a predetermined surface.

BACKGROUND

Optical elements used e.g. in display devices that can be fitted on the head are known from DE 10 2009 010 538 A1.

SUMMARY

An object of the invention includes developing an optical element such that it has improved imaging properties. In addition, a display device with such an optical element is to be provided.

In the optical elements with a Fresnel structure known until now, such as e.g. in DE 10 2009 010 538 A1, all facets have the same surface description and are thus part of the same predetermined surface. The predetermined surface is therefore optimized first and then the optically active facets are produced from it by a modulo operation (parallel offset of parts of the same surface).

According to certain embodiments, in the optical element the predetermined surfaces of the optically active facets (of at least two optically active facets) are different in terms of their curvature profiles. Thus this is not one and the same surface, but each optically active facet is, or the at least two optically active facets are, described by another predetermined surface (which differs from the other surfaces in particular in terms of its curvature profile). It is thereby possible to optimize each optically active facet or the at least two optically active facets separately, whereby the imaging properties of the Fresnel structure can be improved overall. Thus, compared with conventional Fresnel structures, e.g. monochromatic and polychromatic image errors (for example monochromatic transverse aberrations which can be expressed as blurring or ghosting, and transverse chromatic aberrations) can be reduced much better.

The predetermined surfaces can be spherical or aspherical surfaces and preferably have no mirror or rotational symmetry. In addition, it is possible for them to have no translational symmetry. There are thus many degrees of freedom, with the result that a very good optimization can take place, whereby very good imaging properties are provided.

The Fresnel structure is preferably formed on a boundary surface of the optical element.

The boundary surface of the optical element can be formed curved. In particular the optical element has a curved front side and a curved rear side. The front and rear sides can be spherically curved and in particular can be arranged concentrically.

Furthermore, the optical element can have an end face connecting the front and rear sides, which is flat or curved. The Fresnel structure according to the invention can be formed on the end face.

The optical element can be formed as a lens with a refractive power of zero or with a refractive power not equal to zero.

The Fresnel segments can neighbour each other directly, with the result that there is a continuous Fresnel structure. Alternatively it is possible for the Fresnel segments to be spaced apart from each other, with the result that the discontinuous Fresnel structure is present. In this case the original curvature profile of the boundary surface is present between the individual Fresnel segments.

The Fresnel structure preferably provides an optical imaging function.

The optically active facets can bring about a beam deflection by total internal reflection or by reflection. In particular they can be provided with a reflective coating. In addition, the Fresnel segments can be filled with a material such that the area of the Fresnel structure has the same surface profile as a neighbouring area.

The optically active facets of the optical element according to the invention cannot be assembled, by a parallel offset, to form a continuous surface, as the predetermined surfaces of the optically active facets differ in terms of their curvature profile.

In particular the optically active facets cannot be assembled (e.g. by parallel offset) to form a surface which is continuously differentiable. A tilting or another assembling also does not enable the assembled surface then to be continuously differentiable. This assembling is in particular an imaginary assembling which need not be carried out in actuality. The assembling can be carried out computationally if there is a corresponding surface description for each optically active facet. The surface description can be determined for example by a suitable measurement. Conventional Fresnel structures, in which the optically active facets are part of one and the same predetermined surface, can be assembled to form a continuously differentiable surface, in contrast to the Fresnel structure according to the invention.

The optical element can be formed from glass or plastic. The optically active facets are for example formed as pieces of surface. They can have a reflective coating.

In addition to the described formation of the Fresnel structure as a reflective structure, of course, it can also be formed as a refractive structure.

In the optical element according to certain embodiments, the optically active facets can be arranged next to each other along a first direction and extend in the form of strips transverse to the first direction.

Furthermore, it is possible for the optically active facets to be arranged next to each other along a first direction and along a second direction running transverse to the first direction. The Fresnel structure can thus have facets arranged next to each other as desired. The facets can be strip-shaped. They can also have any other shape. In particular, they can be formed as a polynomial with three, four, five or more corners, round, circular, etc. The more facets are provided, the more degrees of freedom there are for the optimization, and the better the optical results that can be achieved.

In the optical element according to certain embodiments, the Fresnel structure can be formed as a reflective Fresnel structure to deflect light bundles incident on the Fresnel structure along a direction of incidence into a direction of emergence, wherein the optically active facets are formed reflective and are arranged next to each other, and at least two directly neighbouring facets in each case have a first reflective section and an adjoining second reflective section, wherein the reflectivity of the first reflective section is greater than the reflectivity of the second reflective section and wherein, viewed in the direction of incidence, the second reflective section of a first reflective facet lies in front of the first reflective section of the directly neighbouring reflective facet, with the result that the part of the incident light bundle that is transmitted by the second reflective section of the first reflective facet strikes the first reflective section of the directly neighbouring reflective facet, in order to be deflected.

Through this partially transparent formation of the facets or through the second sections which are both reflective and transmissive, it is advantageously achieved that the deflected total light bundle which comprises all deflected light bundles has as uniform as possible a brightness distribution.

The first section of the facets can be only reflective or can be partially transparent, and thus both reflective and transmissive.

In the optical element, the second reflective section of the reflective facets can in each case have a first area which adjoins the first reflective section and a second area which adjoins the first area, wherein the second area of the first facet, viewed in the direction of incidence, lies in front of the first area of the directly neighbouring facet. A very homogeneous brightness distribution in the deflected total light bundle can thus be achieved. A light bundle is thus, as a rule, deflected by three facets, namely by the first reflective section of the first facet, the second reflective section of the second facet lying behind this and the second area of the third facet lying behind that.

In particular, the reflectivity of the first area can be greater than the reflectivity of the second area. A very good homogeneity of the brightness distribution in the deflected total light bundle is thus achieved.

In the optical element the Fresnel structure can be formed as a buried Fresnel structure.

In addition, a face which connects two directly neighbouring facets can be formed transparent.

Furthermore, a display device is provided, with an optical element according to certain embodiments, a holder that can be fitted on the head of a user, an image-generating module which generates an image and is secured to the holder, and an imaging optical system which is secured to the holder and which has the optical element and images the generated image, when the holder is fitted on the head, such that the user can perceive it as a virtual image, wherein the image generated by the image-generating module is coupled into the optical element via a coupling-in section of the optical element, guided in the optical element, by one or more reflections (e.g. total internal reflection), to a coupling-out section and coupled out of the optical element via the coupling-out section, wherein the coupling-in and/or coupling-out section has the Fresnel structure. If both the coupling-in and the coupling-out sections have the Fresnel structure, of course, the optical element has two Fresnel structures with several Fresnel segments, wherein each Fresnel segment has an optically active facet the shape of which is part of a predetermined surface which is different for different optically active facets in terms of its curvature profile.

The optical element can in particular be formed in the shape of a spectacle lens with a front side (in particular a curved front side) and a rear side (in particular a curved rear side), wherein when the holder is fitted on the head the front side faces away from the user and the rear side faces towards the user. If the Fresnel structure is formed as a reflective structure, it is preferably formed on the front side. In the formation of the Fresnel structure as a refractive structure, it is preferably formed on the rear side.

The front side of the optical element or of the spectacle lens can be spherically curved. In the same way, the rear side of the optical element or of the spectacle lens can be spherically curved. The radius of curvature of the front side and the rear side can in each case be smaller than or equal to 200 mm, preferably smaller than or equal to 140 mm and in particular smaller than or equal to 100 mm.

The coupling-in section can be formed on the rear side and/or on the end face which connects the front and rear sides.

The generated image can be guided in the optical element by at least two reflections, and thus at least one reflection on the front side and one reflection on the rear side. In order to bring about the reflections, the corresponding sections of the front and rear sides can have a reflective coating or a partially reflective coating. However, it is also possible for one or two reflective or partially reflective layers to be formed within the spectacle lens and for the reflection for guiding the image to take place thereon. In addition, it is possible for the reflections to be brought about on the front and rear sides by total internal reflection. The described types of image guidance by reflection can also be combined with each other.

The coupling-out section is preferably spaced apart from the coupling-in section. In particular the coupling-out section is arranged such that the coupling-out section lies within the visual field of a user when the holder is fitted on.

The image-generating module can in particular have a flat imaging system, such as e.g. an LCD module, an LCoS module or an OLED module. The imaging system can be self-luminous or not self-luminous.

The image-generating module can in particular be formed such that it generates a monochromatic or a multi-coloured image. Of course, the imaging optical system is formed correspondingly in this case.

The display device according to certain embodiments can have further elements known to a person skilled in the art which are necessary for its operation.

Furthermore, a method for producing the optical element according to certain embodiments is provided in which in a step a) an individual surface description is provided for each optically active facet, in a step b) the shape of the surface characterized by the surface description is optimized for each optically active facet, in order to determine the predetermined surface, in a step c) the production data are generated on the basis of the thus-determined predetermined surfaces and in a step d) the optical element is produced on the basis of the production data.

In the method according to certain embodiments, in step c), for each facet, the part of the determined predetermined surface which characterizes the optically active facet can be arranged computationally on a curved base surface.

Furthermore, in the method according to certain embodiments, each Fresnel segment can have a side face connected to the optically active facet and the side face can be designed such that it suppresses scattered light.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the stated combinations but also in other combinations or alone, without departing from the scope of the present invention.

DETAILED DESCRIPTION

In the following descriptions, the present invention will be explained with reference to various exemplary embodiments. Nevertheless, these embodiments are not intended to limit the present invention to any specific example, environment, application, or particular implementation described herein. Therefore, descriptions of these example embodiments are only provided for purpose of illustration rather than to limit the present invention.

In the embodiment shown inFIG. 1, the display device1according to the invention comprises a holder2which can be fitted on the head of a user and which can be formed e.g. in the manner of a conventional spectacles frame, as well as a first and a second spectacle lens3,4which are secured to the holder2. The holder2with the spectacle lenses3and4can be formed e.g. as sports glasses or sunglasses, wherein a virtual image can be reflected into the user's field of view via the first spectacle lens3, as described below. The spectacle lenses3,4are formed such that they have no optical imaging effect, and thus no correction of defective vision takes place.

The right-hand spectacle lens3is formed as an optical element according to the invention with a Fresnel structure21and is described here only by way of example as part of the display device1according to the invention.

As can best be seen from the enlarged detailed sectional view of the first (right-hand) spectacle lens3(the holder2is not represented), the display device1comprises an image-generating module5, a control unit6for controlling the image-generating module5as well as a lens22. The image-generating module5, the control unit6and the lens22are represented purely schematically and are preferably secured to the holder2.

The right-hand spectacle lens3has a spherically curved front side7, a spherically curved rear side8as well as an end face9. The spherical curvatures of the front and rear sides7,8are preferably concentric or almost concentric. The spectacle lens is particularly preferably designed as a meniscus with no refractive power.

The light coming from the image-generating module5is coupled, by means of the lens22, via the end face9into the spectacle lens3such that it is guided multiple times on the front and rear sides8,9(here in each case twice in the areas23,24,25,26) by means of total internal reflection to the Fresnel structure21. The Fresnel structure21is formed on the front side7such that it deflects the light beams in the direction towards an exit pupil14, against which a user has the pupil of his eye when the display device1is fitted on. In the embodiment described here, the Fresnel structure21has, in addition to its function of beam path folding, also an imaging function. In conjunction with the lens22as well as a possibly provided imaging effect of the end face9, the image generated by means of the image-generating module5is presented to the user in the exit pupil14as a virtual image.

The Fresnel structure21thus forms a coupling-out section together with the path through the spectacle lens3to the rear side8, through which the light passes after reflection on the Fresnel structure21. The end face9forms a coupling-in section which optionally also comprises the area of the first reflection on the front side7. Although the Fresnel structure21is part of the coupling-out section in the described embodiment, it can alternatively or additionally be part of the coupling-in section.

As indicated in the enlarged detailed view according toFIG. 3, the Fresnel structure21has several Fresnel segments27which in each case have an optically active facet28on which the light beams are reflected (inFIG. 3the reference numbers28of the facets are also provided with a subscript in order to be able to differentiate between the individual facets in the following description; if no differentiation is necessary, the subscript is omitted). The optically active facets28are connected to each other by side faces29. The facets28extend, as can be seen in the schematic perspective view according toFIG. 4from the direction30according toFIG. 3, substantially in the x-direction, wherein in the representation fromFIG. 4the area of the facets28used as well as a light beam L are represented, in order to indicate the imaging and beam-deflecting effect of the Fresnel structure21.

The shape of each optically active facet28and in particular the cross-sectional shape indicated inFIG. 3is in each case part of a predetermined surface which, however, differs for the individual optically active facets28in respect of the curvature profile. It is thus possible to achieve an imaging property or error correction that is improved compared with conventional Fresnel structures. In conventional Fresnel structures, such as are described e.g. in DE 10 2009 010 538 A1, the shape of the optically active facets is part of one and the same predetermined surface, wherein the facets are only offset in parallel to each other.

In the formation according to the invention of the Fresnel structure21, however, the predetermined surface for the facets28is different from facet28to facet28. There are thus more degrees of freedom for the optimization of the shape of the optically active facets28, whereby for example an improved correction of monochromatic and polychromatic image errors (such as e.g. monochromatic transverse aberrations which can be expressed as blurring or ghosting, or transverse chromatic aberrations) is possible.

Such a formation of the optically active facets28can be achieved in that for each optically active facet28an individual surface description is provided and computationally optimized. In the optimization it is taken into account which beams strike which facets28. It is preferably taken into account whether shadows or misses occur for the individual beams. Thus, for example, in the beam A according toFIG. 3there is the difficulty that this beam, which should strike the facet283, is shadowed by the facet282. In the beam B there is the difficulty that the latter misses the facet281and instead strikes the facet282. These effects are preferably taken into account in the optimization. Thus, a non-sequential ray tracing can e.g. be carried out.

The predetermined surface for each of the optically active facets28can be described by the polynomial specified below:

z⁡(x,y)=∑i,j⁢cij⁢xi⁢yj
The values of the coefficients cjfor the facets28represented schematically inFIG. 4are specified in the following tables, wherein in the tables the facets from right to left inFIG. 1are called facets281,282, . . .2810. In other words the facet281is the facet which is drawn on the far right inFIG. 4.

To describe the optical structure of the display device according to the invention, it is represented inFIG. 5in a similar way to inFIG. 2, wherein in the representation fromFIG. 5essentially only the optically active surfaces are represented schematically. Furthermore the three beam pathes are drawn in for clarification.

The surfaces F1and F2relate to a cover glass of the image-generating module, wherein an imaging system, not shown, is arranged on the surface F1.

The surfaces F3to F8are surfaces of a prism which is provided instead of the lens22represented schematically inFIG. 2.

The surfaces F9, F10and F11are surfaces of the right-hand spectacle lens3. The surface F12is the exit pupil14according toFIG. 2.

The orientations of these surfaces are specified below, wherein it is assumed that the coordinate origin lies in the surface F12, with the result that all specifications below in respect of the surfaces F1-F12relate to this coordinate system. For this, the value of the x, y and z location coordinates in the “location” row is specified for each surface. In addition, the x, y and z directional component of the corresponding surface coordinate system in respect of the surface F12is specified as EX, EY and EZ for each surface.

This is specified in the following table for all surfaces F1-F12as well as all facets281-2810.

The surface F1is thus offset relative to the coordinate system of the surface F12by 56.4602673 mm in the x-direction, by 2.7796851 mm in the y-direction and by 21.6640695 mm in the z-direction. The x-axis (“EX” row) of the surface F1has −0.480488 as x-component, 0.1608098 as y-component and −0.8621319 as z-component in relation to the unit vector. The corresponding component values for the y-axis (“EY” row) and the z-axis (“EZ” row) of this surface F1are correspondingly specified.

Surface F3 Entry into prismLocation55.37623252.342585621.8147278EX−0.49980.1601816−0.8512002EY−0.14580820.9531650.264984EZ0.85377980.256551−0.453036

Surface F9 Entry into spectacle lens via rear side 8, radius 90 mmLocation−0.0000001−0.0000002−15.6995003EX0.9998140.0018171−0.0192EY0.00000010.9955510.0942242EZ0.0192858−0.09420670.9953658

Surface F10 Reflection in the section 23, freeform surfaceLocation24.74809959.5460548−13.3644689EX0.81563920.09257280.5711067EY−0.21247130.96606960.1468519EZ−0.5381344−0.2411220.8076333

Surface F9 Total internal reflection on rear side 8Location−0.0000001−0.0000002−15.6995003EX−0.999814−0.00181710.0192EY0.00000010.9955510.0942242EZ−0.01928580.0942067−0.9953658

Surface F11 Total internal reflection on front side 7, radius 94 mmLocation−0.07714330.3768266−19.6809637EX0.9998140.0018171−0.0192EY0.00000010.9955510.0942242EZ0.0192858−0.09420670.9953658

Surface F9 Total internal reflection on rear side 8Location−0.0000001−0.0000002−15.6995003EX−0.999814−0.00181710.0192EY0.00000010.9955510.0942242EZ−0.01928580.0942067−0.9953658

Surface F9 Exit from spectacle lens 3Location00−15.6995EX0.9998140.0018171−0.0192EY0.00000010.9955510.0942242EZ0.0192858−0.09420670.9953658

The values for the freeform surfaces F8and F10are specified in the following table in the same way as for the facets281-2810.

As can be seen from the above specifications, the light beams enter the prism via the cover glass (surfaces F1and F2) on the surface F3. There is then a reflection on the surface F4, on the surface F3, on the surface F5, on the surface F6, on the surface F7, with the result that the light beams exit from the prism via the surface F8and enter the spectacle lens via the rear side8(surface F9). In the spectacle lens there are then reflections on the front side7and rear side8(surfaces F10, F9and F11), with the result that the light bundles are guided to the Fresnel structure21, on which they are deflected in the described manner in the direction towards the eye, with the result that they exit from the spectacle lens via the rear side8(surface F9) and can be perceived by an eye of the user in the area of the surface F12.

InFIG. 6the pupil of a field point, and thus the imaging of an image pixel into the exit pupil14, is represented in arbitrary units, wherein the different shapes stand for reflection on different facets28.FIG. 6shows that the observed field point is imaged into the exit pupil14by six optically active facets28.

In the optimization of the predetermined surfaces for the optically active facets28it is also possible to allow a shadowing to occur (beam A) or for the beam to miss its original facet (beam B), and then these beams are also taken into account in the optimization of the shape of the predetermined surface. It has been shown according to the invention that in the embodiment example described here it is sufficient to take the directly neighbouring facets28into account.

Furthermore the suppression of undesired stray light can also be taken into account in the optimization. For this, in particular, the shape of the side faces29is altered in respect of the stray light optimization.

The reflection on the facets28can be a total internal reflection. It is also possible for the facets28to be provided with a reflective coating in order to obtain the desired reflection. For example this can be a partially transparent coating, with the result that, in addition to the reflection on the facets28, a certain transmittance is also possible, with the result that the user can perceive the surroundings even in the area of the facets28. Of course, the reflective coating can also be formed such that it is completely reflective and does not transmit any light.

As indicated in the schematic sectional representation inFIG. 7, the free spaces formed by the formation of the facets can be filled, on the front side7, with material31such that the original shape of the front side7is also present in the area of the Fresnel structure21. If the facets28are provided with a reflective coating, the same material can be used for the filling as for the spectacle lens3. If a total internal reflection is desired, a corresponding different material is chosen in which a total internal reflection is possible.

The previously described Fresnel structure21is a continuous Fresnel structure in which the side faces29connect neighbouring facets28. However, it is also possible to form the Fresnel structure21as a discontinuous Fresnel structure21, as indicated inFIG. 8. In this case, the side faces29do not connect two neighbouring facets28, but there is another section of the front side7between the side face29and the neighbouring facet28. These areas are transmissive, with the result that the facets28can be provided e.g. with a reflective coating and a superimposition of the surroundings and the imaged virtual image is still possible even within the Fresnel structure21. The reflection can also take place by total internal reflection in the formation as a discontinuous Fresnel structure21and a material filling can be carried out in the same way as was described in conjunction withFIG. 6. This is thus possible for the case of the total internal reflection and also for the case of the reflective coating.

In the previously described embodiments the facets28are formed strip-shaped or elongate, wherein they are arranged next to each other in a first direction (here the y-direction) and extend in the form of strips in a second direction transverse to the first direction (here approximately the x-direction), as can be seen in particular inFIG. 4. It can also be said that the facets28are arranged next to each other transverse to their longitudinal direction. By the strip-shaped formation of the facets28is meant here in particular that the extent of the facets28is greater in the second direction or in the longitudinal direction (thus here in approximately the x-direction) than in the first direction or in the transverse direction (here the y-direction). In particular the extent in the longitudinal direction is at least twice as great as the extent in the transverse direction.

However, the facets28need not be formed strip-shaped. It is also possible for the facets28to be arranged next to each other along the second direction (here approximately the x-direction). Thus, e.g., the strip-shaped facets according toFIG. 4can be divided in the longitudinal direction, as indicated inFIG. 9. Each of the individual facets is preferably optimized individually. Thus, each of the facets28can be part of a predetermined surface, wherein the predetermined surfaces of the facets28differ in respect of their curvature profile.

In the embodiment shown inFIG. 9the facets28are also formed in principle as elongate or strip-shaped facets28. However, this is not essential. The facets28can have widely different shapes and also need not be arranged regularly, as is indicated inFIG. 10. Preferably, also in the representation according toFIG. 10, each of the facets28is in each case part of a predetermined surface, wherein the predetermined surfaces for the individual facets28differ in respect of their curvature profile. Because the facets28according to the embodiments fromFIGS. 9 and 10are smaller than the facets28according toFIG. 4, small aberrations per facet28will advantageously occur. Because, also, the number of facets28is higher, this can be used as a further degree of freedom in the optimization of the surfaces for the facets28.

InFIG. 11a modification of the optical element according to the invention is shown in a representation which corresponds to the representation according toFIG. 3. In this modification each reflective facet28has a first reflective section32and an adjoining second reflective section33, wherein the reflectivity of the first reflective section32is greater than that of the second reflective section33.

In the embodiment described here the first reflective section32for the light beams L1-L4to be deflected can have as high as possible a reflectivity (for example 100%). The reflectivity of the second reflective section33can be e.g. 50%, with the result that 50% of the incident light is reflected and 50% is transmitted. This advantageously has the result that after the deflection by the Fresnel structure21there are as few as possible to no gaps between the deflected light beams L1-L4and thus there is a homogeneous brightness distribution in the light bundle present through the deflected light beams L1-L4.

In the representation according toFIG. 11three reflective facets28arranged next to each other (which are called first, second and third facets281,282and283here) are represented together with the corresponding light beams L1-L4. In addition, in each of the reflective facets281-283the first reflective section32is shown with a continuous line and the adjoining second reflective section33, which has a lower reflectivity, is represented as a dashed line.

As can be seen from the representation inFIG. 11, the second reflective section33of the first reflective facet281, viewed in the direction of incidence ER, lies in front of the first reflective section32of the second reflective facet282. This has the result that the light beam L2, which strikes precisely the start of the second reflective section33of the first reflective facet281, is partially deflected by the second reflective section33in the direction of the direction of emergence AR and partially transmitted as the light beam L2′. The transmitted light beam L2′ strikes the first reflective section32of the second reflective facet282lying behind the second reflective section33of the first reflective facet281and is deflected by it in the direction of the direction of emergence AR. The area34represented shaded is thus also filled with deflected light beams18, which would not be the case if the second reflective section33of the first reflective facet281had no transmitting property, but was purely reflective. In this embodiment of the right-hand spectacle lens3the section (second reflective section33) of the reflective facet28is thus formed partially reflective and partially transparent, which section would result in a shadowing of the reflective facet28lying behind in the predetermined direction of incidence ER. The undesired gaps after deflection can thus be prevented or filled with the correspondingly deflected light beams.

Furthermore, it is possible for the first reflective sections32not to be purely reflective, but to allow a certain transmittance. This can be utilized e.g. so that the surroundings can also be perceived by the user through the first reflective section32when the display device1is fitted on. The virtual image can in this case be represented superimposed with the surroundings.

A further embodiment of the right-hand spectacle lens3according to the invention is shown in perspective inFIG. 12with three schematically represented reflective facets281,282and283. The shape and position of the facets281-283can be determined, for example, as follows. Light beams L1which strike the lower edge362of the second facet282determine the boundary or boundary line371between the first reflective section32and the second reflective section33of the first reflective facet281. Light beams L2which strike the lower edge363of the third facet283determine the boundary or boundary line372between the first and second reflective section32and33on the second reflective facet282as well as an upper boundary or upper boundary line381on the first reflective facet281.

Beams L3which are reflected at the lower edge363of the third facet283must touch the upper edge391of the first facet281and where possible have the same direction as the beams which are reflected on this upper edge391of the first facet281. The part of the light beam L which is reflected by the upper partial area42of the second reflective section33of the first facet281(shaded) must adjoin the part which is reflected by the first reflective section32of the second facet282. The upper partial area42of the second reflective section33is the area between an upper boundary381and the upper edge391. The upper boundary381is defined by the light beam L2which strikes the lower edge363of the third facet283. The area between upper boundary381and lower boundary371can be called the lower partial area41of the second reflective section33.

On the basis of these conditions it is possible to determine the shape and position of the facets28and the location of the boundaries37,38for a light bundle or a light beam (e.g. for a central light bundle L). All facets28can be different for all boundary lines37,38. If all bundles from the object field are taken into account in this way, it can result in an alteration of the outlines of the facets28and the boundary lines. This can result in gaps and also in an inhomogeneous brightness distribution in the light after deflection. However, this is always much less than would be the case without the partially reflective sections33.

The shaded area of entering light beams shows the distribution of the light on semi-transparent facet parts and the assembling to form a gap-free total bundle after deflection on the Fresnel structure21.

Unlike in conventional Fresnel optical systems for spectacles with data reflection, in which the individual facets of the conventional Fresnel optical system consist of adjoining segments of a surface, in the Fresnel optical systems from the embodiment examples the facets can be formed from any segments of different surfaces, wherein the surfaces are described for example by polynomials with different coefficients. The facets can thus be chosen more freely and can be formed overlapping or spaced apart as desired in the beam path. The optical performance is thereby improved, for example the geometric-optical aberrations or beam deviations are reduced by at least 15%, preferably by 30%. At the same time the refractive power of the Fresnel surface can be increased, for example focal lengths of less than 5000 mm, preferably of less than 1000 mm are possible.

In the described embodiments of the display device1according to the invention the virtual image is coupled into the user's field of view via the right-hand spectacle lens3. Of course, a coupling-in via the left-hand spectacle lens4is also possible. In addition, the display device1can be formed such that information is reflected via both spectacle lenses3,4. The reflection can take place such that a three-dimensional image impression forms.

The spectacle lenses3and4according to the described embodiments have an imaging effect with a refractive power of zero. Of course, the spectacle lenses3,4can also have a refractive power not equal to zero and in particular can be designed to correct defective vision. The spectacle lenses3,4can be produced e.g. from glass or from plastic.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiments. It will be readily apparent to those of ordinary skill in the art that many modifications and equivalent arrangements can be made thereof without departing from the spirit and scope of the present disclosure, such scope to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products. Moreover, features or aspects of various example embodiments may be mixed and matched (even if such combination is not explicitly described herein) without departing from the scope of the invention.