DE102019126282A1 - Camouflaged lattice structures - Google Patents

Abstract

A waveguide (1) is proposed with a partially transparent coupling-in section (1E), with a coupling-out section (1A) spatially spaced apart from the coupling-in section (1E) in the lateral direction, with an essentially transparent coupling section (1E) outside the coupling-in section (1E) and outside the coupling-out section (1A) Base body (2), the transparent base body (2) having a front side (2V) and a rear side (2R), the waveguide (1) in the coupling-in section (1E) having a diffractive coupling-in structure (3), the waveguide (1) has a coupling-out structure (4) in the coupling-out section (1A), the diffractive coupling-in structure (3) being designed to come from an object (6) to be detected and hit a front side (1V) of the waveguide (1) in the coupling-in section (1E) To bend radiation only to a part in such a way that the diffracted part as coupled radiation (SE) in the base body (2) by reflections up to the decoupling section (1A) propagated, wherein the decoupling structure (4) deflects at least part of the coupled radiation (SE) hitting it so that the deflected part as decoupled radiation (SA) from the base body (2) in the decoupling section (1A) via the front side (2V ) or the rear side (2R) of the base body (2) emerges, and wherein the diffractive coupling-in structure (3) has a diffraction efficiency which steadily decreases towards at least one edge of the coupling-in section (1E).

Description

The present invention relates to a waveguide and an apparatus for displaying images.

The problem with video telephony is that the respective interlocutor usually looks at the display on which the interlocutor is shown. However, the corresponding camera is usually installed on the edge of the display, outside the image reproduction area of the display. This is often perceived by the interlocutors as a lack of eye contact. In addition, there is a need to be able to use mobile devices for displaying images for video telephony.

Proceeding from this, the present invention is based on the object of specifying a waveguide and a device for image reproduction with which a more natural and immersive conversation experience can be achieved.

This problem is solved with the subject matter of the main claim and the subsidiary claim. Advantageous refinements are given in the subclaims.

A waveguide is proposed with a, in particular partially transparent, coupling-in section, with a coupling-out section spatially spaced apart from the coupling-in section in the lateral direction, with a base body which is essentially transparent outside the coupling-in section and outside the coupling-out section, the transparent base body having a front side and a rear side wherein the waveguide in the coupling-in section has a diffractive coupling-in structure, the waveguide having a coupling-out structure in the coupling-out section, the diffractive coupling-in structure being set up to only partially absorb radiation coming from an object to be detected and hitting a front side of the waveguide in the coupling-in section to bend that the diffracted part propagates as coupled radiation in the base body through reflections, in particular total reflections, up to the coupling-out section, the coupling-out structure of of the coupled radiation hitting it deflects at least a part in such a way that the deflected part emerges as coupled radiation from the base body in the coupling section via the front side or the rear side of the base body, and wherein the diffractive coupling structure has a diffraction efficiency which decreases steadily at least towards one edge of the coupling section having.

The waveguide can have a substantially plate-like shape. The terms front and rear can denote the two surfaces of the plate-shaped waveguide which have the largest surface area. Lateral can denote a direction essentially perpendicular to the front side and / or the rear side. A viewer will look essentially perpendicularly at the front of the waveguide. The radiation striking the front of the waveguide from an object to be detected, for example the radiation coming from an observer, is only partially diffracted so that the diffracted part propagates as coupled radiation in the base body through reflections to the coupling-out section. Conversely, the diffractive coupling-in structure in the coupling-in section also acts for radiation which is directed onto the rear side of the waveguide in the direction of the viewer. For the viewer looking at the waveguide, the coupling-in section thus appears to be shaded from the rest of the front side of the essentially transparent base body. As will be explained below, it can be provided in embodiments that the diffractive coupling-in structure has a diffraction efficiency that steadily decreases towards the edge of the coupling-in section. With this measure, the transition from the shadowed area to the remaining area of the waveguide can be made softer, so that the shadowing is less visible to the observer. A steadily decreasing diffraction efficiency denotes a diffraction efficiency curve without visible jumps which can be perceived as annoying by a viewer. Diffraction efficiency denotes the ratio between the radiation coupled in by diffraction and the radiation coming from the object to be detected and striking the front side of the waveguide in the coupling section.

In a first embodiment, the diffractive coupling structure can have an imaging effect. The imaging effect can consist in the fact that radiation coming from the object to be detected and hitting the front side of the waveguide in the coupling section is coupled into the waveguide as a plane wave. The imaging effect can in particular be a collecting effect. The diffractive coupling-in structure can have a collecting effect in particular in a sectional plane which is arranged perpendicular to the front side of the waveguide and extends through the center of the coupling-in section and the center of the coupling-out section. The imaging effect can be described, for example, with a focal length f ' _E. The imaging effect can in particular correspond to the collecting effect of a cylindrical lens. The coupling structure can also have a collecting effect in more than one level. The focal length f ' _E can for example be between 200 mm and 1000 mm, in particular between 300 mm and 800 mm, in order to avoid radiation from an object which is at a distance of approx mm to 1000 mm away from the front of the waveguide, to be coupled into the waveguide as a plane wave.

In a second embodiment, the diffractive coupling structure in a central section of the coupling section has a diffraction efficiency of more than 0.1 (more than 10%). This can be sufficient to be able to detect the decoupled radiation exiting in the decoupling section. The diffraction efficiency of the diffractive coupling structure in the central section is preferably more than 0.2 (more than 20%). Particularly in poor light conditions, for example twilight, a diffraction efficiency in the central section of more than 0.4 (more than 40%) can prove to be advantageous in order to guide a sufficient amount of light from an object to be detected to the coupling-out section.

In a further embodiment, the diffractive coupling structure in one or the central section of the coupling section has a diffraction efficiency of less than 0.6 (less than 60%). This can make it possible to minimize the shadowing effect described above and to ensure sufficient transmission of radiation directed onto the rear side of the waveguide in the direction of the viewer.

The diffraction efficiency of the diffractive coupling-in structure at an edge of the coupling-in section can in particular be close to zero (0). This can further reduce the noticeability of the transition from the coupling-in section to the remaining region of the waveguide.

Furthermore, an embodiment of the waveguide provides that the diffraction efficiency has a Gaussian or a super Gaussian course. A Gaussian curve is understood to mean a curve that satisfies the following formula: $$\eta \left(x\right)=\mathrm{A.}{e}^{-\frac{{\left(x-b\right)}^2}{2{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="DE102019126282A1\_0003.png"\; state="\{\{state\}\}">c</figure-callout>}}^2}}$$

A supergaussian course is understood to mean a course of the diffraction efficiency which satisfies the following formula: $$\eta \left(x\right)=\mathrm{A.}{e}^{-{\left(\frac{{\left(x-b\right)}^2}{2c^2}\right)}^P}$$

Here, η (x) indicates the diffraction efficiency η as a function of the location x.

The use of a supergaussian course can ensure that the same, high diffraction efficiency is present in a wide area of the coupling-in section, with the diffraction efficiency decreasing evenly towards the edge of the coupling-in section at the same time.

In a further embodiment, the diffractive coupling structure is designed as a relief grating. Relief gratings can be manufactured particularly easily, which means that the manufacture of the waveguide can be cheaper. In a similar form, the coupling-out structure can also be designed as a relief grating. The coupling-in structure and the coupling-out structure can in this case also be referred to as coupling-in relief grating or coupling-out relief grating.

To realize the imaging effect of the diffractive coupling structure, the grating period can vary slightly but continuously over the coupling section.

In one embodiment, a profile depth of the coupling-in grating that decreases towards the edge leads to the diffraction efficiency that decreases towards the edge. The profile depth of the coupling relief grating can be easily influenced during the production of the relief grating.

Alternatively or in addition, a profile shape of the coupling relief grating that changes towards the edge can also lead to the diffraction efficiency decreasing towards the edge. With a changing profile shape, the diffraction of radiation that comes from the object to be detected, but which does not strike the front of the base body perpendicularly, can be favorably influenced.

The coupling-in relief grating can in particular comprise a blaze grating. In this case, a gradient of the blaze grating that changes towards the edge can lead to the diffraction efficiency decreasing towards the edge.

In principle, it is also conceivable to design the diffractive coupling structure as a reflective or transmissive volume hologram. A diffraction efficiency that decreases towards the edge can then be achieved by modulation of the refractive index that decreases towards the edge. As an alternative or in addition, a layer thickness of the volume hologram could also be varied in this case. The use of a material for the transmissive volume hologram which has a similarly high refractive index as the waveguide can lead to a high proportion of the diffracted part, which propagates as coupled radiation in the base body.

The diffractive coupling-in structure and / or the coupling-out structure can be designed as a diffractive coupling-in structure or coupling-out structure buried in the base body. The formation of the diffractive coupling-in structure and / or the coupling-out structure on or in a surface of the base body has proven to be particularly advantageous in terms of production technology. The diffractive coupling-in structure can advantageously be designed as a coupling-in relief grating on the rear side of the base body and / or the coupling-out structure as a coupling-out relief grating on the front side of the base body. The coupling-in relief grating and / or the coupling-out relief grating is preferably incorporated directly in the high-index material of the base body and not as a separate polymer layer applied to the base body, in which the relief grating is molded. This can help reduce the number of process steps required to manufacture the waveguide. In addition, almost inevitable radiation losses can be avoided at interfaces between different materials.

The base body can be provided with a coupling-in coating on its rear side, at least in the coupling-in section, the material of which has a refractive index that is higher than the refractive index of the material from which the base body is made. In that case, the coupling-in coating can be provided in particular on a surface of the coupling-in relief grating. The coupling coating can further increase the diffraction efficiency. Titanium dioxide, in particular, comes into consideration as the material for the coupling-in coating. This material can be applied particularly easily to a base body and has a high refractive index.

In the coupling-in section, the layer thickness of the coupling-in coating can vary in order to lead to the diffraction efficiency decreasing towards the edge of the coupling-in section. Diffraction efficiency may decrease in areas with a thinner coating.

The coupling-in coating can in particular be a vapor-deposited layer.

In a further embodiment, the base body is provided with a coupling-out coating on its front side, at least in the coupling-out area. The coupling-out coating can make it possible for almost all of the coupled-in radiation to be coupled out. The coupling-out coating can in particular be a metal coating, preferably an aluminum coating. In order to increase the mechanical and chemical resistance of the metal coating, the metal coating can also be provided with a dielectric protective layer on the side facing away from the base body.

Another embodiment provides that the base body is made from a polymer with a refractive index greater than or equal to 1.50, in particular greater than or equal to 1.60, in particular greater than or equal to 1.74. The refractive indices relate to a wavelength of 546.07 nm (e-line). At other wavelengths, different refractive indices may arise.

Such polymers are also known under the term high refractive index polymer (HRIP). The base body can in particular be made from an episulfide resin. For example, the base body can be made from a material sold by Mitsui Chemicals, Inc. under the designation MR-174®.

In contrast to the use of glass for the base body, the choice of a polymer makes it possible to provide a lighter base body. This is consequently also better suited for use in a mobile device for displaying images.

In principle, it is also desirable to have the largest possible angular range in which total reflection conditions are met in the base body in order to be able to couple radiation coming from the object in a large angular range by means of the coupling structure. The use of a polymer with a refractive index greater than 1.6 for the base body can make it possible to choose a non-gaseous material in front of and behind the base body, following the base body, without the total reflection conditions being destroyed. This can further simplify the structural design of the waveguide.

When using a polymer with a refractive index greater than 1.74 for the base body, even with a non-gaseous material adjoining the base body, an angular range for total reflection can be achieved which almost corresponds to that of the material sequence air-glass-air. Typically, an air gap in front of the base body is difficult to implement in mobile devices for image reproduction, since a touch sensor, e.g. a touchpad, is regularly arranged in front of the waveguide. When the touch sensor is touched, a force is exerted on the touch sensor that cannot be derived from the air gap. Accordingly, the touch sensor must be designed to be very robust and therefore heavy, so that forces that occur can be diverted via the edges of the touch sensor. The above-described waveguide thus allows the manufacture of a lighter mobile device for image display that includes a touch sensor.

The coupling relief grating and / or the decoupling relief grating can be formed by reshaping the Base body be made in the base body. For example, the coupling-in relief grating and / or the coupling-out relief grating can be introduced into the base body by hot stamping. This can be accomplished very easily by means of a stamp which has a surface structure that is complementary to the coupling-in relief grating or the coupling-out relief grating. In this case, a plate-shaped base body made of a high-index polymer can be used as the starting material, which can be manufactured simply and in high quality with a uniformly high transparency. In contrast to a base body made of glass, a coupling relief grating can easily be embossed into a base body made of a high-index polymer.

It is also conceivable to introduce the coupling-in relief grating and / or the coupling-out relief grating into the base body by at least one etching process. For this purpose, a mask can first be applied to the base body, then via an in particular directed etching process (e.g. sputtering), material of the base body for producing the coupling relief grating or decoupling relief grating can be removed and finally the etching mask can be removed.

In this case, only a plate-shaped material has to be made available for the base body.

Alternatively, the base body can be produced together with the coupling-in relief grating and / or with the coupling-out relief grating by reshaping. For example, the base body with the coupling-in relief grating and / or with the coupling-out relief grating can be produced by injection molding. The coupling-in relief grating or the coupling-out relief grating can be formed by an insert of the shape which has a surface structure that is complementary to the coupling-in relief grating or the coupling-out relief grating.

It is also conceivable, for example, to form the decoupling relief grating when the base body is originally formed and the coupling relief grating then by reshaping the base body. Likewise, when the base body is originally formed, the coupling-in relief grating can first be produced and then the prefabricated base body can be provided with the coupling-out grating by reshaping.

According to a further embodiment it is provided that a rear side adhesive layer composite with at least one first rear side adhesive layer is arranged on the rear side of the base body and / or the coupling coating, and that the first rear side adhesive layer is arranged on the side of the rear side adhesive layer composite facing the base body. The rear side adhesive layer composite can also consist only of the first rear side adhesive layer.

The first adhesive backing layer can be made from a material with a refractive index less than or equal to 1.329, in particular less than or equal to 1.324, preferably less than or equal to 1.319, in order to improve that of the radiation coupled into the base body.

Furthermore, the rear side adhesive layer composite can have a second rear side adhesive layer, wherein the second rear side adhesive layer is arranged on the side of the first rear side adhesive layer facing away from the base body, and wherein the second rear side adhesive layer is made of a material with a refractive index that is greater than the refractive index of the material from which the first adhesive backing layer is made.

The second rear side adhesive layer can in particular serve to connect the waveguide to a further element and thereby compensate for stresses due to a different coefficient of thermal expansion of the first rear side adhesive layer and the further element.

The first adhesive backing layer can be made from an adhesive that has come into liquid contact with the base body and / or the coupling coating. For example, the adhesive can simply be applied to the prefabricated base body and then cured, for example by UV radiation or heat. This can happen in particular after the waveguide has been connected to the further element with the still liquid adhesive. Alternatively, a liquid adhesive can also be provided which hardens itself after a certain time. Such adhesives can include, for example, two-part adhesives.

In another embodiment, a front side adhesive layer composite can also be arranged on the front side of the base body. The front-side adhesive layer composite can likewise have a first front-side adhesive layer and / or a second front-side adhesive layer. In particular, the first front-side adhesive layer can be made from the same material as the first rear-side adhesive layer and the second front-side adhesive layer can be made from the same material as the second rear-side adhesive layer. The first front-side adhesive layer is typically also arranged on the side of the front-side adhesive layer composite facing the base body. The front-side adhesive layer composite can also consist only of the first front-side adhesive layer.

The first adhesive backing layer and / or the second adhesive backing layer can in particular be produced from a polymer that consists of 1 to 15% by weight of aliphatic urethane acrylate and 85 to 99% by weight of acrylic monomer. Examples of such polymers are those under the name Norland Optical Adhesive 1315 (trade code: NOA 1315), Norland Optical Adhesive 132 (trade code: NOA 132) and Norland Optical Adhesive 1327 (trade code: NOA 1327) from Norland Products Inc. available.

A device for image reproduction with a waveguide as described above is also proposed, the device comprising a display with an image reproduction surface, the display being connected to the display by means of the rear adhesive layer composite, the coupling-out section being arranged outside the reproduction surface of the display, and the coupling-in section is arranged within the image reproduction area of the display.

The display can in particular be a transmassive or a reflective display. Examples of the suitable displays mentioned here are LCD displays or OLED displays.

In one embodiment of the device for image reproduction, the device for image reproduction comprises a camera arranged outside the image reproduction surface, the camera having at least one sensor for detecting the coupled-out radiation. For example, the camera can be attached next to the display on the back of the waveguide.

The sensor of the camera can be, for example, a CMOS sensor or a CCD sensor. The camera can also include a lens.

A beam trap can be attached to the front and / or the rear of the waveguide outside the image reproduction area between the display and the coupling-out section. The beam trap can minimize the risk of light from the display reaching the camera's sensor.

The device for displaying images can in particular be a smartphone, a tablet computer, a desktop computer, a notebook computer, a video telephone or a terminal device of an intercom system.

• 1 und 2 eine Seitenansicht einer Ausführungsform der Vorrichtung zur Bildwiedergabe;
• 3 einen Transmissionsverlauf und einen Intensitätsverlauf um den Einkoppelabschnitt herum;
• 4 Beugungseffizienzverläufe um den Einkoppelabschnitt herum.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawings. From the figures show:

• 1 and 2 a side view of an embodiment of the device for image reproduction;
• 3 a transmission curve and an intensity curve around the coupling section;
• 4th Diffraction efficiency curves around the coupling section.

1 shows an apparatus for displaying images 10 . In the exemplary embodiment shown, the device is for image reproduction 10 to a smartphone. The device for displaying images 10 includes a waveguide 1 . The waveguide has a partially transparent coupling section 1E and one from the coupling section 1E in the lateral direction spatially spaced decoupling section 1A on.

Outside the coupling section 1E and outside of the coupling-out section 1A the base body is essentially transparent. In this context, essentially transparent means that light comes from the back 2R of the base body unhindered in front of the front 2V arranged viewer 6th can reach. In particular, essentially transparent can mean that light comes from an image reproduction surface of a display 11 , the viewer 6th can reach. Smaller non-transparent areas can be used, for example, for mechanical fastening of the base body 2 be provided. The waveguide 1 has a diffractive coupling structure in its coupling-in section 3 on.

The diffractive coupling structure 3 is in the embodiment shown as a coupling relief grating 3 designed. The very schematically shown coupling relief grating 3 is a blaze grid.

The base body 2 can for example be made of a high-index polymer. The coupling-in relief grating can then be in a surface, in particular the rear side 2R of the base body 2 be brought in. This can be done, for example, by hot stamping using a stamp which has a surface structure that is complementary to the coupling-in relief grid.

The waveguide points further 1 the coupling-out section 1A a coupling-out structure 4th on. Also the decoupling structure 4th is designed as a relief grid, namely as a decoupling relief grid.

The diffractive coupling structure 3 is set up from an object to be detected 6th , which in the present case is a viewer 6th acts, coming and in the coupling section 1E on a front 1V of the waveguide 1 to bend the incident radiation only to a part so that the diffracted part as coupled radiation SE in the base body 2 through reflections up to the decoupling section 1A propagated.

The decoupling structure 4th directs at least part of the coupled radiation that hits it SE so that the deflected part as decoupled radiation SA from the base body 2 in the decoupling section 1A over the back of the base body 2 exit. In principle, it is also conceivable that the coupled-out radiation SA over the front 2V of the base body emerges.

The forwarding of part of the from the object 6th in the coupling section 1E on the waveguide 1 hitting radiation SO via the coupling structure 3 and the base body 2 to the decoupling section 1A can also be referred to as a periscope function.

On the back side 2R of the base body 2 is a coupling coating 5 intended. The refractive index of the material of the coupling coating 5 is higher than the refractive index of the material from which the base body 2 is made. The coupling coating 5 does not only extend over the coupling relief grating 3 but over the entire back 2R of the base body 2 .

The waveguide 1 furthermore has a rear side adhesive layer composite 8th on, the one on the coupling coating 5 is arranged. The backside adhesive layer composite 8th comprises a first adhesive backing layer 81 on that of the base body 2 facing side of the rear side adhesive layer composite 8th . The first adhesive backing layer is made from a material with a refractive index less than 1.48, more precisely from a material with a refractive index less than or equal to 1.315.

The use of a first rear side adhesive layer made of a material with a refractive index less than or equal to 1.315 allows in combination with the use of a material for the base body 2 with a refractive index of 1.74 an angle range of 49.1 ° to 90 ° that can be used for total reflection. This corresponds almost to an angular range of a waveguide which is made of glass and borders on air.

The rear side adhesive layer composite also has 8th a second adhesive backing layer 82 on. The material of the second rear side adhesive layer is preferably selected in such a way that it eliminates thermally induced stresses due to different coefficients of thermal expansion of the rear side adhesive layer composite 8th can balance connected elements.

The waveguide 1 is by means of the rear side adhesive layer composite 8th with a display 11 connected. In the present case it is the display 11 around an OLED display. However, it is also possible to use an LCD display. Due to the transparency of the base body 2 can a viewer 6th that from the display 11 perceive the displayed image. At the same time, that of the viewer 6th radiation coming from the coupling structure 3 in the base body 2 coupled into the coupling-out structure 4th propagated and decoupled there again.

The back of the decoupling structure 4th , ie the back of the decoupling relief grating 4th , is provided with a coupling-out coating. The coupling-out coating 7th , which can be a metal coating, in particular an aluminum coating, ensures that the largest possible part of the radiation is coupled out. The coupled out radiation SA can from the sensor of the camera 12th can be detected. In this case, in addition to the sensor, the camera also includes only indicated, imaging optics between the coupling-out structure 4th and the sensor. Hence the direction in which the viewer is corresponding corresponds 6th that from the display 11 perceived image and the direction from which the viewer perceives 6th with the camera 12th is recorded. The result is a more natural conversation experience for the viewer.

On the front side 2V of the base body 2 is a front side adhesive layer composite 9 provided, which is also the decoupling coating 7th covered. In to the rear side adhesive layer composite 8th The front side adhesive layer composite comprises correspondingly 9 also a first front-side adhesive layer 91 and a second front adhesive layer 92 . The first front adhesive layer 91 can be made of the same material as the first adhesive backing layer 81 . This can in particular the total internal reflection properties of the waveguide 1 receive. The second front adhesive layer 92 In contrast, it can be made of a material that simplifies the connection with other elements.

In the present case, there is an adhesive layer composite in front of the front side 9 a touch sensor 16 intended. This can be used to operate the device for image reproduction 10 serve. Instead of the touch sensor 16 In principle, however, a simple transparent cover plate, for example made of glass, can also be provided around the waveguide 1 to protect against external influences.

On the front and the back of the waveguide 1 is in the lateral direction between the display 11 and the coupling-out section 1A one beam trap each 14th and 15th appropriate. The ray traps 14th and 15th prevent light from the display through reflections on the camera's sensor 12th so that the camera 12th prefers only that of the viewer 6th incoming light is detected. With the same aim are laterally on the front sides of the base body 1 Beam traps, in the present case as light-absorbing coatings 13th and 17th are formed, provided. Furthermore, the coupling grating structure 3 optimized for that from the display 11 sent out and by coupling structure 3 likewise unavoidably diffracted light essentially in one of the coupling-out section 1A away, ie in the 1 and 2 Bend to the right, facing direction. In particular the beam trap / light-absorbing coating 17th can be the back reflection at that end of the waveguide 1 / Base body 2 reduce to a minimum.

From the object to be detected, the viewer 6th , coming radiation SO is in the coupling section 1E of the waveguide 1 by means of the coupling structure 3 only partly as coupled radiation SE into the waveguide 1 bent. The coupled radiation 1E is then in the waveguide 1 guided by total reflection.

The ratio of the power of the coupled radiation SE in terms of the total from the viewer 6th coming radiation SO is 1:10 in the exemplary embodiment shown. This is indicated by the fact that the arrows for the coupled-in radiation SE only one-tenth the width of the arrow for the whole of the viewer 6th coming radiation SO are shown.

In the 2 is again already in the 1 Device shown for image reproduction 10 shown, some reference numerals have been omitted for the sake of clarity.

In contrast to the 1 is in the 2 that emitted from the display by the viewer 6th through the transparent waveguide 1 perceived radiation SD , SH shown.

The effect of the coupling structure 3 is not limited to radiation SO taken by the viewer 6th comes. Rather, the coupling structure 3 in the coupling section 1E also the transmission of radiation from an object behind the waveguide 1 reduced in the direction of the viewer 6. With even illumination through the one behind the waveguide 1 lying display 11 reduced from the viewer 6th perceived radiation SH in the coupling section 1E . This is again shown by an arrow with a reduced width.

In contrast to the usual optimization of a blazed grating with regard to maximum efficiency with regard to the useful diffraction order, the coupling-in relief grating designed as a blazed grating can be used 3 be optimized to the proportion of the display 11 incoming light, which in the direction of the decoupling structure 4th is bent to minimize.

The ratio of the difference between the radiation coming from the display SD and the one in the direction of the viewer 6th in the coupling section 1E from the waveguide 1 outgoing service SH as well as that of the display 11 coming radiation SD can, in a first approximation, essentially be the ratio between the coupled-in radiation SE and that of the object 6th coming radiation SO correspond.

The greater the proportion of the coupled radiation SE in terms of from the object 6th coming radiation SO the more that becomes of the display 11 The image shown is shaded in the coupling section.

In which that is on the display 11 Image to be displayed for all locations outside the coupling section 1E lie opposite the points within the coupling section 1E is darkened, the local shading effect is caused by the diffractive coupling structure 3 compensated. This is in 3 shown.

In 3 a) is a section of the display 11 as well as the waveguide 1 with the diffractive coupling structure 3 around the coupling section 1E shown around. The diffraction efficiency η of the coupling structure 3 has in the entire coupling section 1E a constant value.

In the 3 b) is a schematic of the course of the transmission T of the waveguide 1 shown as a function of location X. The transmission from the display is between x ₁ and x ₂ 11 to the front 1V of the waveguide 1 due to the diffractive coupling structure 3 degraded. Outside this coupling section 1E the transmission can be, for example, 90% (0.9) and within the coupling-in section 1E , ie between x ₁ and x ₂ , 80% (0.8).

In the 3 c) the intensity I is that of the display 11 emitted radiation in the area of the coupling section 1E reproduced. For example, between points x ₁ and x ₂ , the intensity is 100% (1). Outside of the range it is decreased to about 88.8% (0.888). For a perpendicular to the device for displaying images 10 or the display 11 looking viewer 6th appears on the display 11 the displayed image is thus homogeneous.

Looks the viewer 6th but not perpendicular to the display 11 is shifted by the coupling structure 3 shaded area in relation to the display 11 and the image represented by this, as the coupling structure 3 and the display 11 do not lie in one plane. This is in the 3 b) indicated with dashed and dotted lines.

In the edge area of the coupling section 1E is the compensation of the shadowing effect of the diffractive coupling structure made for a specific viewing angle 3 not effective for other viewing angles. Rather, they arise in the edge area of the coupling-in section 1E strong fluctuations in brightness caused by the viewer 6th can be perceived as annoying. The brightness fluctuations that occur for different viewing angles can also be referred to as parallax errors. They can also occur when the viewer 6th although perpendicular but at a relatively small distance to the device for image reproduction 10 looks, since every eye of the beholder 6th at a slightly different angle on the coupling section 1E is directed.

In the 4 a) is again a section of the device for image reproduction 10 in the area of the coupling section 1E shown. In the 4 b) is the diffraction efficiency η of the diffractive coupling structure 3 shown as they are the remarks on 3 underlying. It has a constant value between the points x ₁ and x _2. This value of the diffraction efficiency η can be, for example, 10% (0.1). Takes the diffraction efficiency η of the diffractive coupling structure 3 , like in the 4 c) shown, from a maximum value of 10% (0.1) in the middle between the points x ₁ and x ₂ to the edge of the coupling section 1E steadily, this leads to an approximation of the value of the transmission T in the coupling-in section 1E to the value outside the coupling section 1E so that a jump in brightness from the viewer 6th can hardly be perceived even at different viewing angles.

Thus, the shadowing effect can be achieved by the diffractive coupling structure 3 by evenly adjusting the intensity of the display 11 emitted radiation SD can be compensated without any perceptible brightness fluctuations in the edge area of the coupling-in section when the viewing angles change 1E occur. This can prove to be particularly advantageous when the diffractive coupling-in structure 3 not at the back 2R of the base body 2 is provided, but as a buried coupling structure within the base body 2 . With a buried coupling structure 3 A viewing angle dependency of the compensation can be particularly noticeable, since the distance between the diffractive coupling structure 3 and the display 11 is typically larger than one at the rear 2R of the base body 2 arranged diffractive coupling structure 3 .

As a result, the proposed configuration of the device allows for image reproduction 10 that the diffractive coupling structure 3 from a viewer 6th are not perceived and thus one can speak of a camouflaged lattice structure.

List of reference symbols

1

Waveguide

1E

Coupling section

1A

Decoupling section

1R

Back of the waveguide

1V

Front of the waveguide

2

Base body

2V

Front of the base body

2R

Back of the base body

3

diffractive coupling structure, coupling relief grating

4th

Outcoupling structure, outcoupling relief grating

5

Coupling coating

6th

Object, viewer

7th

Outcoupling coating

8th

Rear side adhesive layer composite

81

first backside adhesive layer

82

second backside adhesive layer

9

Front side adhesive layer composite

91

first front side adhesive layer

92

second front side adhesive layer

10

Device for displaying images, smartphone

11

Display

12th

camera

13.17

light absorbing coating

14.15

Ray trap

16

Touch sensor

SE

coupled radiation

SA

coupled radiation

SO

from the object 6th coming radiation

SD

from the display 11 radiated from the viewer 6th outside the coupling section 1E perceived radiation

SH

from the display 11 radiated from the viewer 6th radiation perceived within the coupling section

Claims (14)

Waveguide (1) with a partially transparent coupling section (1E), with one spatially spaced from the coupling-in section (1E) in the lateral direction Decoupling section (1A), with one outside the coupling-in section (1E) and one outside the coupling-out section (1A) essentially transparent base body (2), wherein the transparent base body (2) has a front side (2V) and a rear side (2R), the waveguide (1) in the coupling-in section (1E) having a diffractive coupling-in structure (3) having, wherein the waveguide (1) in the coupling-out section (1A) has a coupling-out structure (4), the diffractive coupling-in structure (3) being designed to be detected by one Object (6) coming and in the coupling section (1E) on a front side (1V) of the waveguide (1) to bend radiation only to a part so that the diffracted part as coupled radiation (SE) in the base body (2) by reflections up to propagated to the decoupling section (1A), the coupling-out structure (4) from the coupled-in radiation (SE) incident on it deflects at least one part in such a way that the deflected part emerges as decoupled radiation (SA) from the base body (2) in the decoupling section (1A) via the front side (2V) or the rear side (2R) of the base body (2), and wherein the diffractive coupling structure (3) at least one edge of the Coupling section (1E) has steadily decreasing diffraction efficiency. Waveguide (1) according to Claim 1 , characterized in that the diffractive coupling structure (3) has an imaging, in particular a collecting, effect. Waveguide (1) according to one of the preceding Claims 1 or 2 , characterized in that the diffraction efficiency (η) has a Gaussian or a super Gaussian course. Waveguide (1) according to one of the preceding claims, characterized in that the diffractive coupling structure (3) is designed as a coupling relief grating (3) and / or that the coupling out structure (4) is designed as a coupling relief grating (4). Waveguide (1) according to Claim 4 , characterized in that a profile depth of the coupling relief grating (3) decreasing towards the edge leads to the diffraction efficiency (η) decreasing towards the edge. Waveguide (1) according to one of the preceding Claims 4 or 5 , characterized in that a profile shape of the coupling relief grating (3) which changes towards the edge leads to the diffraction efficiency (η) decreasing towards the edge. Waveguide (1) according to one of the preceding Claims 4 to 6th , characterized in that the coupling relief grating (3) comprises a blaze grating (3). Waveguide (1) according to Claim 7 , characterized in that a slope of the blaze grating (3) which changes towards the edge leads to the diffraction efficiency (η) decreasing towards the edge. Waveguide (1) according to one of the preceding claims, characterized in that the diffractive coupling-in structure (3) and / or the coupling-out structure (4) is designed as a coupling-in structure (3) or coupling-out structure (4) buried in the base body (2) or that the diffractive coupling-in structure (3) and / or the coupling-out structure (4) is formed on a surface of the base body (2). Waveguide (1) according to one of the preceding claims, characterized in that the base body (2) is provided with a coupling coating (5) on its rear side (2R) at least in the coupling section (1E), that the refractive index of the material of the coupling coating (5) is higher than the refractive index of the material from which the base body (2) is made. Waveguide (1) according to one of the preceding claims, characterized in that on the rear side (2V) of the base body (2) and / or the coupling coating (5) a rear side adhesive layer composite with at least one first rear side adhesive layer is arranged, that the first rear side adhesive layer on the Base body (2) facing side of the rear side adhesive layer composite is arranged. Device for image reproduction (10), characterized in that the device for image reproduction (10) comprises a waveguide (1) according to one of the preceding claims, that the device comprises a display (11) with an image reproduction surface (11E), that the display ( 11) is connected to the display by means of the adhesive backing layer, so that the coupling-out section (1A) is arranged outside the image reproduction surface (11E) of the display (11), that the coupling section (1E) is arranged within the image reproduction surface (11E) of the display (11). Image reproduction device (10) according to Claim 12 , characterized in that the device for image reproduction (10) comprises a camera (12) arranged outside the image reproduction surface (11E), that the camera (12) has at least one sensor for detecting the coupled-out radiation (SA). Image display device (10) according to one of the preceding Claims 12 or 13th , characterized in that the device is a smartphone, a tablet computer, a desktop computer, a notebook computer, a video telephone or an intercom device.

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