The present invention relates to a display device including a holding device that can be worn on the head of a user and an image-generating module which generates an image and is attached to the holding device and a method for producing a multifunction glass of such a display device as well as an optical element having an optically effective surface which at least in part has a Fresnel structure with several Fresnel segments.
An optical element with a Fresnel structure is often used to reduce installation space, for example in the case of illumination lens systems. In this case, e.g. rotationally symmetric Fresnel structures as well as toric Fresnel structures are used.
A rotationally symmetric Fresnel lens which is used in transmission for light reflection and optical imaging in back projection devices is known from U.S. Pat. No. 6,989,992 B2. A rotationally symmetric Fresnel lens working in reflection and having concave Fresnel structures which is used in an illumination lens system is known from U.S. Pat. No. 7,178,947 B2. A Fresnel structure working in reflection which serves to shape rays and starting from a cylindrical profile shape is further known from U.S. Pat. No. 4,510,560.
With display devices according to the type named at the beginning, the problem often arises of coupling the generated image into the multifunction glass such that it is guided in the latter to the coupling-out area without disruptive image errors occurring.
Starting from this, the object of the invention is to improve the display device of the type named at the beginning such that the coupling-in takes place such that disruptive image errors are avoided as far as possible. Furthermore, a production method for a multifunction glass of such a display device is to be provided.
The object is achieved in the case of a display device of the type named at the beginning in that the coupling-in area comprises a Fresnel structure which brings about a folding of the beam path during the coupling of the image into the multifunction glass and has an imaging property.
The coupling-in can thus be carried out such that the image is guided in the multifunction glass to the coupling-out area (for example by total internal reflection). Furthermore, disruptive image errors can be effectively countered by means of the imaging property.
The Fresnel structure can be formed in particular at a material boundary surface of the multifunction glass, wherein the material boundary surface is in particular a curved material boundary surface. A great freedom of design for the multifunction glass is thus provided which is hardly or not at all limited by the necessary optical function of the coupling-in area, as the optical function of the coupling-in area is effected by means of the Fresnel structure.
The Fresnel structure can be formed transmissive or reflective. If it is formed transmissive, it is preferably formed on the material boundary surface of the multifunction glass facing the image-generating module. If the Fresnel structure is reflective, it is preferably formed on the material boundary surface of the multifunction glass facing away from the image-generating module.
The Fresnel structure can have several Fresnel segments, wherein the optically effective facets of the Fresnel segments optically correspond to an imaginary optical effective surface which is curved and has neither mirror symmetry nor rotational symmetry. Furthermore, the optical effective surface preferably also has no translational symmetry. With such an optical effective surface, the desired folding of the beam path, and the desired imaging property, can be realized even if the Fresnel structure is formed on a material boundary surface of the multifunction glass that is curved.
The maximum height of each facet is preferably the same in the case of the Fresnel structure. It lies, for example, in the range of 5-500 μm, in another example in the range of 0.01-0.1 mm. A range of 200-300 μm and a range of 0.05-0.3 mm are used in another example embodiment.
The facet shape can be an approximation, in particular a linear approximation to the shape of the corresponding surface section of the imaginary effective surface. In particular, the facets can be concave or convex in cross-section.
The Fresnel segments can be directly neighbouring, as is the case with a “standard” Fresnel structure. However, is it possible that the Fresnel segments are spaced apart from each other, wherein the normal course of the material boundary surface is then present between them.
A method for producing a multifunction glass of a display device according to the invention is furthermore provided in which a Fresnel structure which has an imaging property as well as a folding property for the beam path is formed in the coupling-in area of the multifunction glass.
With this method, a multifunction glass for the display device according to the invention and thus also the display device according to the invention itself can be easily produced.
In the production method, the Fresnel structure can be formed on a curved material boundary surface of the multifunction glass. Thus, a coupling of the design of the multifunction glass itself (of its shape and curvature) can virtually be carried out by its coupling-in area. As soon as the shape of the multifunction glass is fixed, the Fresnel structure for the coupling-in area can be calculated and manufactured.
In the method, the Fresnel structure can have several Fresnel segments, wherein the optically effective facets of the Fresnel segments are formed such that they optically correspond to an imaginary optical effective surface which is curved and has neither mirror nor rotational symmetry. In particular, the optical active surface also has no translational symmetry.
In the production method according to the invention, the multifunction glass can be produced on the basis of production data which are generated computationally by dividing an optical model surface into several height regions and computationally arranging the surface sections of the individual height regions or approximation of these surface sections at a base surface such that they optically correspond to the optical effective surface. The division into the several height regions can take place at a constant height or also at varying heights. In particular, the height lies in the range of 5-500 μm as well as in the range of 0.01-0.1 mm. A range of 200-300 μm and a range of 0.05-0.3 mm are particularly preferred.
The height regions can in particular be chosen such that the distance to the base surface is constant in each case.
The surface sections or the approximation of the surface sections can be arranged computationally at a flat or at a curved base surface. In particular, the arrangement of a curved base surface is advantageous, as in this case the material boundary surface of the multifunction glass can also be curved. A linear approximation is carried out in particular as approximation of the surface sections. However, any other type of approximation is also possible.
The facets can be formed such that the maximum height of all the facets is the same.
In particular, the production method according to the invention can be developed such that the multifunction glass of the display device according to the invention (including all developments) can be produced.
Furthermore, an optical element with an optically effective surface which at least in part has a Fresnel structure with several Fresnel segments is provided, wherein the optically effective facets of the Fresnel segments optically correspond to an imaginary optical effective surface which is curved and have no mirror or rotational symmetry.
The optical element can thus be used in widely different fields. In particular, the optical element can be formed as a multifunction glass of the display device according to the invention.
Such an optical effective surface which has neither mirror nor rotational symmetry and is also called free-form surface in the following can initially be computationally optimized independently of its spatial extent, in order that the then-manufactured optical element with the Fresnel structure has the desired properties. The spatial extent of the free-form surface plays no role in practice in the implementation of the free-form surface as a Fresnel structure, as it can be provided in an optically equivalent manner by the individual facets, with the result that the above-mentioned computational optimization can be carried out.
The maximum facet height can be predetermined and for example lie in the range of 5-500 μm, in particular in the range of 0.01-0.1 mm. A range of 200-300 μm and a range of 0.05-0.3 mm are particularly preferred.
The optical effective surface preferably also has no translational symmetry.
In particular, the optically effective surface is a boundary surface of the optical element. This facilitates the production of the optical element. Thus, it can for example be produced by diamond milling. However, it is also possible to produce the optical element by moulding and casting methods.
The Fresnel segments can be formed as reflective or as refractive segments. In the case of reflective formation, the reflectivity can be adjusted and lie in a range of from more than 0 to almost 100%.
In particular, the maximum height of each facet in the case of the optical element can be the same.
Furthermore, the facet shape can be an approximation, in particular a linear approximation to the shape of the corresponding surface section of the imaginary effective surface. Thus, an optically corresponding action can still always be achieved. Of course, the optical action of the Fresnel structure is in reality not identical to the optical action of the imaginary optical effective surface. According to the invention, it is essential that the deviation of the actual optical action of the Fresnel structure from the optimum optical action of the imaginary optical effective surface is so small that the optical element meets the optical requirements set, as is always the case with optical elements, which in reality never achieve the theoretical maximum optical action.
The facets can be curved concavely or also convexly in cross-section.
Furthermore, the Fresnel segments can be directly neighbouring. However, it is also possible that individual Fresnel segments are spaced apart from each other.
The optically effective surface with the Fresnel structure is in particular a continuous surface.
Furthermore, a method for producing the optical element with an optically effective surface which at least in part has a Fresnel structure with several Fresnel segments is provided, in which the optically effective facets of the Fresnel segments are formed such that they optically correspond to an imaginary optical effective surface which is curved and has no mirror or rotational symmetry.
With this production method, an optical element with excellent optical properties can be produced.
The optical effective surface can also in particular have no translational symmetry.
The Fresnel segments are preferably formed at a boundary surface of the optical element. This simplifies the production of the optical element.
The optical element can be produced on the basis of production data which are generated computationally by dividing an optical model surface into several height regions and computationally arranging the surface sections of the individual height regions or approximations of these surface sections at a base surface (e.g. on or under the base surface) such that they optically correspond to the optical effective surface. The division into the several height regions can take place at a constant height or also at varying heights. In particular, the height lies in the range of 5-500 μm or in the range of 0.01-0.1 mm. A range of 200-300 μm and a range of 0.05-0.3 mm are particularly preferred.
The height regions can in particular be chosen such that the distance to the base surface is constant in each case.
The surface sections or the approximation of the surface sections can be arranged computationally at a flat or at a curved base surface.
In particular, a linear approximation can be chosen as an approximation of the surface sections. However, any other type of approximation is also possible.
The facets can be formed such that the maximum height of all the facets is the same.
In particular, the production method according to the invention can be developed such that the optical element according to the invention and its developments can be produced.
The optical element can be used for example as a beam splitter or also as a beam combiner. Furthermore, the optical element can be used as a deflecting element. It is also possible to form the optical element as an imaging element that operates reflectively or refractively. Further possible designs are given in the following embodiments. The optical element can thus also be used in the field of HMD (Head Mounted Display) devices.
It is understood that the features mentioned above and those yet to be explained in the following are applicable, not only in the given combinations, but also in other combinations or singly, without departure from the scope of the present invention.
The invention is explained in further detail below by way of example using the attached drawings which also disclose features essential to the invention. There are shown in:
In the embodiment shown in
Each Fresnel segment 4 has an optically effective facet 5. In order to achieve the stepped shape shown in
The common optical action of the facets 5 corresponds to an imaginary optical effective surface 8, such as is shown in
The active surface 8 is divided in z-direction into sections of equal height Δh. Section lines 9 which can also be called contour lines and which each delimit a surface section 10 of the active surface 8 thereby result. The surface sections 10 are all shifted in z-direction towards each other such that in each case the lower section line (the one with the lower z-value) and thus the lower rim of the facet 5 lie at the same height (in z-direction). The perpendicular edge 6 is then guided from the respective upper section line of the surface sections 10 and thus the upper rim of the facet 5 to the lower section line of the directly neighbouring surface section 10, in order to arrive at the stepped formation of the Fresnel structure 3 according to
The steps that are to be carried out in order to arrive at the desired Fresnel structure 3 from the imaginary optical effective surface 8 which is curved and does not have mirror or rotational symmetry are explained in detail below in conjunction with
It can be seen in the enlarged representation of the detail C in
Thus, the following Formula 1 can be presented for the Fresnel structure 3, wherein zF describes the Fresnel structure 3, Zbase
Z
F
=Z
base
surface
+z
facet (1)
The surface Zfacet of the facets, which can also be called “Fresnelled” free-form surface, is calculated according to the following Formula 2:
Z
facet=modulo(zeffective
wherein the effective surface 8 is described by the following surface formula Zeffective
in which K1 denotes the conical term in x-direction and K2 the conical term in y-direction, as is given below
By applying the modulo function to the effective surface 8, the effective surface 8 is divided in z-direction into distances of equal height Δh. Thus, the maximum height of the facets 5 is Δh in each case. The modulo function used is given below:
wherein the Gaussian brackets
denote the largest whole number that is smaller than or equal to the number in the Gaussian brackets, thus the result of the division a/m without the remainder of the division. The following formula thus results for the facet surfaces
According to the above-described procedure, the corresponding Fresnel structure 3 which provides the corresponding optical action can be deduced on the basis of a desired optical effective surface 8 which is curved and has no mirror or rotational symmetry and is also called free-form surface 8 below. Although the same optical action that a lens whose base surface is formed according to the free-form surface 8 would have cannot be achieved with the Fresnel structure 3 because of the stepped shape, a comparable optical action is achieved.
As can be seen from the representation in
With this procedure according to the invention allowing any free-form surface 8 to be formed on a flat surface as a Fresnel structure, a design optimized in terms of installation space is possible for example.
Thus for example a Fresnel mirror 1 can be produced such as is shown in
The Fresnel structure 3 can be based for example on the free-form surface 8 shown in
In this embodiment example, the following can be given as base surface function of Formula 1: zbase
In the previously described embodiment examples, in each case a flat surface or a plane was assumed as base surface. Of course, it is also possible to provide a base surface differing from this if e.g. the Fresnel structure 3 is to be formed on a spherically curved lens upper surface. In this case, a fine tuning can virtually be carried out by means of the Fresnel structure 3 in the manner that e.g. further aberrations of the lens or the group of lens systems in which the lens is used are corrected.
As shown in
An example is shown in
An example is shown in
Z
base
surface
=R−sgn(R)√{square root over (R2−x2−y2)} (8),
wherein R is the radius of curvature of the spherical base surface 17, and sgn(R)=1, if R>0 (i.e. convex surface), sgn(R)=−0.1, if R<0 (i.e. concave surface), sgn(R)=0 for R=0. For the effective surface Zeffective
wherein k(i,j) is determined as follows:
0.01 mm was adopted as the depth of the Fresnel structure 3 or crimping in z-direction and thus for the value Δh. Furthermore, M=8 and N=8 were used. The following Fresnel polynomial coefficients thus result
All unnamed coefficients k(i,j) which are not listed in the above table are equal to 0. The radius R of the spherical mirror is (−)50 mm here.
The allocation between the indices i, j, k can also be given by the following matrix:
wherein j runs horizontally from 0-5 and i perpendicularly from 0-5 and the allocated matrix values give the corresponding k-index value.
In
In
Z
F
=Z
base
surface
−Z
facet (12)
This way of calculating zF is of course also possible in all the already described embodiments as well as in all the embodiments still to follow.
In
A Fresnel structure 3 shown according to
Because of the arrangement of the imaging system 25, an image ray beam BS enters the multifunction glass 1 via the back 36 and strikes the Fresnel structure of the deflecting element 38 which brings about a deflection of the image ray beam BS to the left, with the result that the image ray beam BS is guided in the multifunction glass 1 on the basis of total internal reflection at the back 36 as well as at the front 28 to a superimposition area 29 in which the image ray beam BS is superimposed on the surrounding radiance US to form a common ray beam GS. The superimposition takes place such that, in a pupil area P, the image generated by means of the imaging system 25 is perceptible for a user superimposed on the surroundings.
As can be seen from the schematic side view in
In
As can be seen from the representation in
The deflecting element 38 here is a coupling-in section or area via which the image of the imaging system 25 is coupled into the multifunction glass 1 such that the image ray beam BS is guided to the superimposition or coupling-out section 29 by means of total internal reflections. For this, the deflecting element brings about a folding of the beam path and has an imaging property.
The multifunction glass 1 has a spherically curved, convex front 8 with a radius of 143.5 mm as well as a spherically curved, concave back 36 with a radius of curvature of 140.0 mm, wherein the thickness of the eyeglass lens is 3.5 mm and PMMA was used as material for the eyeglass lens.
The Fresnel structure of the deflecting element 38 can be given in the same way as the reflective Fresnel structure 3 on the mirror 16 with spherical base surface 17 according to
All unnamed coefficients k(i,j) which are not listed in the above table are equal to 0.
The Fresnel structure for the coupling-out section or area 29 can also be described by means of Formulae 8 to 10. The corresponding Fresnel polynomial coefficients are given in the following table, wherein again all unnamed coefficients k(i,j) which are not listed in the table are equal to 0.
Also in the case of the Fresnel structure of the coupling-out section 29, Δh is equal to 0.1 mm.
The position of the optical surfaces in the overall coordinate system of the pupil P of the eye A (the point of origin is at K) can be given as follows by reference to the direction of the coordinates x, y and z in
In the case of the coupling-in and coupling-out sections 38 and 29, the position of the coordinate system is given, with regard to which the Fresnel surface is defined in the manner given above. In each case, values of 0 are therefore given for the surface 38, as the coordinate systems for the surfaces 29 and 38 coincide. The position and size of the used aperture surface of the respective Fresnel surface, which corresponds to the coupling-in section 38 and to the coupling-out section 29, are as follows with regard to the coordinate system peculiar to the surface:
In this table, the width of the Fresnel structure in x-direction is given in the APX column and the width of the Fresnel structure in y-direction in the APY column. Furthermore, the distance of the coupling-out section 38 from the coupling-in section 29 is given. The distance from the eye pupil P to the eyeglass lens (back 38) here is 18 mm, wherein the field of vision is 20×4° for a diameter of 6 mm.
Variants of the display device 22 according to
The formation of the coupling-in and coupling-out sections 38, 29 as well as optionally the deflecting section 38′ on the same side of the multifunction glass 1 (here on the front 28) facilitates the production of the multifunction glass 1.
In
In
However, it is also possible to design the Fresnel structure 3 such that the deflection of the image ray beam BS takes place by total internal reflection, with the result that a metallization is no longer necessary, as is indicated in
A sectional view of a further Fresnel structure 3 is shown in
All Fresnel structures 3 described thus far have been continuous Fresnel structures. By this is meant that the individual Fresnel facets 5 are always connected to each other by the edges 6. However, it is also possible to provide the Fresnel facets 5 spaced apart from each other and insert sections 23, which can for example be sections of the base surface 11, between the individual Fresnel facets 5. This can easily be realized by replacing areas or sections of the determined Fresnel surface zF with the course of the base surface Zbase
If the Fresnel facets 5 are metallized, a beam combiner 1 for example can be provided in this way, such as is represented in an enlarged sectional view in
The part of the surrounding ray beam US which strikes the back of the Fresnel facets 5 (from the left in
The discontinuous Fresnel structure 3 according to
The superimposition area 29 of the multifunction glass 1 from
For this, the Fresnel segments are preferably formed (as reflective Fresnel segments) e.g. in circular sectors 40, such as is shown in the schematic top view on the, for example rectangular, superimposition area 29 in
In order to prevent a regular arrangement or structure of the Fresnel sections, these can e.g. be arranged as follows. Circular areas are fixed, the diameter of which can be determined as follows
D=√{square root over ((100−T)/100/π)}·2·APX/N
Wherein T is the required transmission for the surrounding light in percent, N the number of the circles in x-direction and APX the aperture width in x-direction. The circles are initially arranged equidistant in a fixed grid with a grid spacing APX/N in x and y. The positions of the centres of the circles are then easily modified, by dicing the direction and length of the displacement of the centres. The length is chosen here such that no overlapping effect occurs between neighbouring circles.
The following formulae can be applied as statistical functions for length and angle.
Statistical displacement length:
r=(APX/N/2−D/2)·randf
Statistical displacement direction:
w=360·randf
Wherein randf provides a random value between 0 and 1. The modified position of the circles 40 then results according to the following formulae:
x=(i/N)·APX+r·cos(w)
y=(j/N)·APX+r·sin(w)
M=round(APY/APX)
Wherein the round function rounds the criterion (APY/APX) up to whole numbers.
Of course, any other type of distribution of the Fresnel structure can also be chosen, wherein an irregular arrangement is preferably chosen.
Of course, the beam combiner from
A variant of the beam splitter from
A variant is shown in
In
An optical element 1 which is formed as a beam splitter is shown in
In the versions in
Number | Date | Country | Kind |
---|---|---|---|
102009010538.7 | Feb 2009 | DE | national |
This application is a continuation of application Ser. No. 13/203,203, filed Sep. 22, 2011, which is a National Phase entry of PCT Application No. PCT/EP2010/052426, filed Feb. 25, 2010, which claims priority to German Application Number 102009010538.7, filed Feb. 25, 2009, the disclosures of which are hereby incorporated by reference herein in their entirety.
Number | Date | Country | |
---|---|---|---|
Parent | 13203203 | Sep 2011 | US |
Child | 13895049 | US |