TECHNICAL FIELD

The present disclosure relates to the field of Augmented Reality (AR). In particular, the disclosure provides an optical device for an AR device, which can reduce undesired crosstalk in the AR device. Further, the disclosure provides the AR device and a method for providing an AR using the optical device.

BACKGROUND

AR uses a digital platform to overlay a virtual content onto the real world. The virtual content is typically in the form of videos, text, or images. AR aims to enhance the user experience by bringing digital closer to the human senses. The users may use phones, tablets, or headset to view the world using AR.

An AR display module based on a diffractive waveguide is a popular solution, which consists of two optical engines and two diffractive waveguides.

As to the assembly, in order to create a high fidelity 3D image, the images created by the left and right eye should overlap with each other. When using a double display (one optical engine and one waveguide for each eye), the assembly must be done accurately, as the tolerance on the position and rotation for each display module is small.

In one conventional approach, an optical delivery system provides a sequential left and right image of the display. The illumination is switched for left and right accordingly, using exit pupil expander (EPE) with asymmetric, e.g., highly slanted, in-coupling gratings, to send light practically into only one direction (e.g., one area of the EPE substrate). However, the incoupler is for left and right, which means that the grating must be slanted, to eliminate crosstalk to the left (right) eye from the right (left) optical engine. Further, the waveguide should cover RGB color (red, green, blue), which is a very wide band, and the field of view (FOV) should satisfy the real scenario requirements (i.e., generally larger than 30 degree). Therefore, this solution results in serious crosstalk, which cannot be eliminated by the slanted grating completely. As a result, both eyes may see the same image in a certain region, resulting in a loss of the 3D effect.

SUMMARY

In view of the above-mentioned problems and disadvantages of the conventional approaches, embodiments of the present disclosure aim to provide an improved optical device for an AR device, in particular to overcome the above-described crosstalk between the two eyes. Thereby, a high quality 3D effect of the AR device shall be ensured. Another objective is to reduce a volume and cost of the AR device. One aim is also to reduce packaging difficulties and to improve the efficiency of the assembly of the AR device.

The objectives are achieved by the embodiments of the disclosure as described in the enclosed independent claims. Advantageous implementations of the embodiments of the disclosure are further defined in the dependent claims.

A basic concept underlying embodiments of the disclosure is to separate light into two portions, before the light goes into the waveguide. Thereby, it may be the case that the light at one particular time point is not divided, but that the light in a continuous time period is divided into two portions in time domain. Each incoupler couples only one portion of the light into the waveguide, particularly for guidance along a certain light path. The two portions of the light may be further diffracted to outcouplers, which are configured to couple the light out of the waveguide to the eyes of a user. This may ensure elimination of the diffracted light to the undesired side, which helps to reduce undesired crosstalk.

A first aspect of the disclosure provides an optical device for an AR device, wherein the optical device comprises: a waveguide adapted to guide light towards the AR device; a first incoupling element, configured to receive a first portion of light and to couple the first portion of the light into the waveguide for guidance along a first light path; a second incoupling element, configured to receive a second portion of light and to couple the second portion of the light into the waveguide for guidance along a second light path; the first outcoupling element, configured to receive at least partly the first portion of the light guided along the first light path, and to couple the received light out of the waveguide; the second outcoupling element, configured to receive at least partly the second portion of the light guided along the second light path, and to couple the received light out of the waveguide.

The waveguide may be a double-eye waveguide, e.g., a waveguide that makes up an AR Glass display module. The incoupler of the AR device provided by the optical device maybe divided into two part, i.e., into the first incoupling element and the second incoupling element, respectively, for coupling two different portions of light into two different directions (along two different light paths). Notably, the light may be propagated into the first incoupling element and the second incoupling element time sequentially. That is, the time-sequential light may be switched between the two incoupling elements, wherein all the light enters one of the incoupler element at one time.

In an implementation form of the first aspect, a central region of the first incoupling element and a central region of the second incoupling element are arranged along a first axis, wherein the first axis is perpendicular to the incoming light.

Notably, the light may be generated by a light generator, such as a light projector. The generated light may be directly into surfaces of the incoupling elements.

In an implementation form of the first aspect, the first incoupling element is configured to direct the first portion of the received light into a first direction along an axis perpendicular to the first axis; and/or the second incoupling element is configured to direct the second portion of the received light into a second direction along an axis perpendicular to the first axis.

In a conventional design, the waveguide incoupler is arranged in a horizontal direction such as left and right. Notably, the left and right may be relative to a position of an AR device when a user is wearing it. This implementation form modifies the conventional waveguide incoupler arrangement to a vertical direction such as top and bottom. The top and bottom may be relative to the position of the AR device when the user is wearing it. That is, when the AR device is at a position as to be worn by the user, one incoupling element may be located on top of (above) the other one. Such design may prevent light entering the opposite EPE area. For instance, one incoupling element may diffracts a portion of light to the right EPE area, and another incoupling element may diffract another portion of light to the left EPE area. This could effectively reduce undesired crosstalk between two directions.

In an implementation form of the first aspect, the first direction is antiparallel to the second direction.

This is to eliminate the diffracted light from one side to the other side.

In an implementation form of the first aspect, the optical device further comprises a first expansion element and/or a second expansion element, first expansion element being configured to direct the first portion of the light at least partly from the first incoupling element along the first light path and towards the first outcoupling element along an axis parallel to the first axis; the second expansion element being configured to direct the second portion of the light at least partly from the second incoupling element along the second light path and towards the second outcoupling element along an axis parallel to the first axis.

After the EPE area, particularly through the two separated expansion elements, two portions of the light will propagate to the output area and then be diffracted to the eyes of the user.

In an implementation form of the first aspect, the first expansion element comprises a first part and a second part, wherein the first incoupling element is configured to direct the first portion of the light at least partly towards the first part of the first expansion element, the first part of the first expansion element is configured to receive at least partly the first portion of the light direct from the first incoupling element, and direct the received light at least partly towards the second part of the first expansion element, and the second part of the first expansion element is configured to receive at least partly the light from the first part of the first expansion element, and to direct the received light at least partly towards the first outcoupling element.

Each expansion element may be further divided into two parts, for instance, into a left expansion element and a right expansion element. The corresponding incoupling element may diffract the light up or down first, to one part of the expansion element. Then, the light can be diffracted from one part of the expansion element to the left or right side, i.e., to the other part of the expansion element. This design may further help to eliminate the diffracted light to the undesired side.

In an implementation form of the first aspect, the first part of the first expansion element is arranged along the first light path and between the first incoupling element and the second part of the first expansion element.

In an implementation form of the first aspect, a central region of the first part of the first expansion element is arranged along the first axis, and the first part of the first expansion element is configured to direct the received light at least partly towards the second part of the first expansion element along an axis perpendicular to the first axis.

In particular, the first part of the first expansion element may be placed on top of the first incoupling element. In this case, the first incoupling element may till the light up, to the first part of the first expansion element. Then, the light may be further diffracted from the first part of the first expansion element to the second part of the first expansion element, e.g. to the right side for instance.

In an implementation form of the first aspect, the second expansion element comprises a first part and a second part, wherein the second incoupling element is configured to direct the second portion of the light at least partly towards the first part of the second expansion element, the first part of the second expansion element is configured to receive at least partly the second portion of the light direct from the second incoupling element, and to direct the received light at least partly towards the second part of the second expansion element, and the second part of the second expansion element is configured to receive light from the first part of the second expansion element, and to direct the received light at least partly towards the second outcoupling element.

Alternatively, or additionally, the second expansion element may also be divided into two parts. Notably, there may be only one of the first and the second expansion elements is divided into two parts. In such case, the left eye side and the right eye side of the waveguide may have different architectures. However, the architectures for the left eye and the right eye could be exchanged. In an implementation form of the first aspect, the first part of the second expansion element is arranged along the second light path and between the second incoupling element and the second part of the second expansion element.

In an implementation form of the first aspect, a central region of the first part of the second expansion element is arranged along the first axis, and the first part of the second expansion element is configured to direct the received light towards the second part of the second expansion element along an axis perpendicular to the first axis.

In particular, if the second incoupling element is the incoupling element located at the bottom (below the first incoupling element), the first part of the second expansion element may be placed at the bottom of the second incoupling element. In this case, the second incoupling element may guide the light down to the first part of the second expansion element. Then, the light may be diffracted from the first part of the second expansion element to the second part of the first expansion element, i.e., to the left side for instance.

In an implementation form of the first aspect, the optical device further comprises a first retroreflector and/or a second retroreflector, wherein the first retroreflector is configured to absorb light from the first incoupling element that are directed to a direction other than the first direction, and/or to receive light from the first incoupling element that are directed to a direction other than the first direction, and to direct it at least partly to the first incoupling element; and/or wherein the second retroreflector is configured to absorb light from the second incoupling element that are directed to a direction other than the second direction, and/or to receive light from the second incoupling element that are directed to a direction other than the second direction, and to direct it at least partly to the second incoupling element.

In this way, the first retroreflector and/or the second retroreflector may recycle or absorb the light to the undesired side, and thus may further reduce the crosstalk.

A second aspect of the disclosure provides a AR device comprising: a light engine, configured to generate a first portion of light and a second portion of light; an optical device according to the first aspect or any of its implementation forms, wherein the light coupled out of the waveguide by the first outcouphng element and the second outcouphng element is directed to the eyes of a user of the AR device.

In an implementation form of the second aspect, the AR device is configured to: generate light that is time-sequential, and divide the light into the first portion and the second portion.

Optionally, the light source may be separated into two parts. Notably, time-sequential light may be switched between the two incoupling elements. It is worth mentioning that at different time points only a part of the LED could be lit on, which means that only one of the incoupling elements (i.e., the first incoupling element and the second incoupling element) may work at one time instant.

A third aspect of the disclosure provides a method for guiding light towards an AR device, the method comprising: providing of an optical device according to the first aspect or any of its implementation forms; receiving a first portion of light and a second portion of light; guiding the received light at least partly along a first light path and a second light path; and coupling the received light out of the waveguide and towards the AR device.

A fourth aspect of the disclosure provides a method for providing an AR, the method comprising: generating a first portion of light and a second portion of light related to a virtual image; providing the generated first portion of the light to the first incoupling element, and the generated second portion of the light to the second incoupling element, of an optical device according to the first aspect or any of its implementation forms; and providing of the optical device according to the first aspect or any of its implementation forms.

It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

FIG. 1 shows a schematic of an optical device according to an embodiment of the disclosure.

FIG. 2 shows a schematic of an optical device according to an embodiment of the disclosure.

FIG. 3 shows a schematic of an optical device according to an embodiment of the disclosure.

FIGS.4a-b show K-Vector charts of the optical device of FIG. 3 according to an embodiment of the disclosure.

FIG. 5 shows a schematic of an optical device according to an embodiment of the disclosure.

FIG. 6 shows a light engine according to an embodiment of the disclosure.

FIG. 7 shows an AR device according to an embodiment of the disclosure.

FIG. 8 shows a method according to an embodiment of the disclosure.

FIG. 9 shows a method according to an embodiment of the disclosure. DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the disclosure provide solutions to reduce undesired crosstalk in the optical elements. To this end, this disclosure proposes to separate light into two portions before the light goes into the waveguide. It is further proposed to modify a conventional waveguide incoupler arrangement, by means of splitting the conventional waveguide incoupler arrangement to two separate incoupling elements. This ensures an elimination of diffracted light to the undesired direction.

In particular, FIG. 1 shows, to this end, an optical device 10 according to an embodiment of the disclosure. The optical device 10 is for an AR device 100 such as an AR glass (e.g., as it is shown in FIG. 7). The optical device 10 is shown in a front view along the z-axis, wherein the perpendicular x-, y-, and z-axes form a (Cartesian) coordinate system.

The optical device 10 comprises a waveguide A, which is adapted to guide light towards the AR device 100. The waveguide A may be arranged for both eyes, and may be formed by or in a display glass, e.g., a display glass of a head mounted display (HMD). Further, the optical device 10 comprises a first incoupling element 101, a second incoupling element 111, a first outcoupling element 103, and a second outcoupling element 113.

The first incoupling element 101 is configured to receive a first portion of light 11. For instance, the first portion of light 11 may be received from a light generation engine 20 as shown in FIG. 1, such as an optical projector. Further, the first incoupling element 101 is configured to couple the first portion of the light 11 into the waveguide A for guidance along a first light path, e.g., the path as shown in the right side of FIG. 1.

The second incoupling element 111 is configured to receive a second portion of light 12, e.g., from the same light generation engine 20 that generates the first portion of light 11. Further, the second incoupling element 111 is configured to couple the second portion of the light 12 into the waveguide A for guidance along a second light path, e.g., the path as shown in the left side of FIG. 1.

The first outcoupling element 103 is configured to receive at least partly the first portion of the light 11 guided along the first light path. Further, the first outcoupling element 103 is configured to couple the received light out of the waveguide A, e.g., to the eyes of a user of the AR device 100. Notably, since the light transmitted in the waveguide A may have loss, the lights guided along the light path may at least partly arrive at each optical element.

The second outcoupling element 113 is configured to receive at least partly the second portion of the light 12 guided along the second light path. Further, the second outcoupling element 113 is configured to couple the received light out of the waveguide A. Similar as the first outcoupling element 103, the received light may be coupled out to the eyes of the user of the AR device 100.

In an embodiment of the disclosure, preferably, a central region of the first incoupling element 101 and a central region of the second incoupling element 111 may be arranged along a first axis, e.g., the y-axis as shown in FIG. 1. Notably, the incoming light, i.e., the first portion of the light 11 and the second portion of the light 12, may be from a light generation engine 20 along the z-axis as shown in FIG. 1, so that the first axis may be perpendicular to the incoming light. Notably, the generated light may be directly into surfaces of the incoupling elements.

Optionally, the first incoupling element 101 may be configured to direct the first portion of the received light 11 into a first direction along an axis perpendicular to the first axis. In particular, the first direction may be the x-direction. Optionally, the second incoupling element 111 may also be configured to direct the second portion of the received light 12 into a second direction along an axis perpendicular to the first axis. For instance, as shown in FIG. 1, the second direction may be go along the x-axis in a negative direction.

That is, the first direction may be antiparallel to the second direction, as shown in FIG. 1.

It should be noted that, in this disclosure, an incoupler of the optical device may be divided into two parts, namely the first incoupling element 101 (e.g., a top incoupling element as shown in FIG. 1) and the second incoupling element 111 (e.g., a bottom incoupling element as shown in FIG. 1). As the example depicted in FIG. 1, the top incoupling element would diffract the light to right, while the bottom coupler would diffract the light to left. Compared with a conventional solution in which the incoupler is arranged at the left and right (e.g., in a horizontal direction), the design proposed in this disclosure (i.e., arranging the incoupling elements at the top and bottom in a vertical direction) ensures elimination of the diffracted light from one side to the other side, which effectively helps to reduce undesired crosstalk.

Notably, all the light will be further propagated to the output area and then diffract to the eyes of the user (e.g., of the AR device 10).

According to an embodiment of the disclosure, the optical device 10 may further comprise a first expansion element 102 and/or a second expansion element 112.

Optionally, the first expansion element 102 may be configured to direct the first portion of the light 11 at least partly from the first incoupling element 101 along the first light path. In particular, the first expansion element 102 may be configured to direct the first portion of the light 11 at least partly towards the first outcoupling element 103 along an axis parallel to the first axis. Notably, said axis may be along the y-axis in a negative direction.

Similarly, the second expansion element 112 may be configured to direct the second portion of the light 12 at least partly from the second incoupling element 111 along the second light path. In particular, the second expansion element 112 may be configured to direct the second portion of the light 12 at least partly towards the second outcoupling element 113 along an axis parallel to the first axis. Notably, said axis may be along the y- axis in a negative direction as well.

Further, the expansion element may be divided into two parts.

FIG. 2 shows an optical device 10 according to an embodiment of the disclosure, which builds on the embodiment shown in FIG. 1. Same elements in FIG. 1 and FIG. 2 share the same reference signs and function likewise.

In this embodiment of the disclosure, the first expansion element 102 may comprise a first part 102a and a second part 102b. In particular, the first incoupling element 101 may be configured to direct the first portion of the light 11 at least partly towards the first part 102a of the first expansion element 102. Further, the first part 102a of the first expansion element 102 may be configured to receive at least partly the first portion of the light 11 direct from the first incoupling element 101, and to direct the received light at least partly towards the second part 102b of the first expansion element 102. Then, the second part 102b of the first expansion element 102 may be configured to receive at least partly the light from the first part 102a of the first expansion element 102, and to direct the received light at least partly towards the first outcoupling element 103.

As shown in FIG. 2, the first part 102a of the first expansion element 102 may be arranged along the first light path and between the first incoupling element 101 and the second part 102b of the first expansion element 102.

In particular, a central region of the first part 102a of the first expansion element 102 may be arranged along the first axis. Optionally, the first part 102a of the first expansion element 102 may be configured to direct the received light at least partly towards the second part 102b of the first expansion element 102 along an axis perpendicular to the first axis. For instance, the first part 102a of the first expansion element 102 may be placed on top of the first incoupling element 101. The first part 102a of the first expansion element 102 may diffract the light coming from the bottom (i.e., from the first incoupling element 101) to the top and then to the right (i.e., to the second part 102b of the first expansion element 102).

FIG. 3 shows an optical device 10 according to an embodiment of the disclosure, which builds on the embodiment shown in FIG. 1. Same elements in FIG. 1 and FIG. 3 share the same reference signs and function likewise.

In this embodiment of the disclosure, the second expansion element 112 may comprise a first part 112a and a second part 112b. In particular, the second incoupling element 111 may be configured to direct the second portion of the light 12 at least partly towards the first part 112a of the second expansion element 112. Further, the first part 112a of the second expansion element 112 may be configured to receive at least partly the second portion of the light 12 direct from the second incoupling element 111, and to direct the received light at least partly towards the second part 112b of the second expansion element 112. Then, the second part 112b of the second expansion element 112 may be configured to receive light from the first part 112a of the second expansion element 112, and to direct the received light at least partly towards the second outcoupling element 113. As shown in FIG. 3, the first part 112a of the second expansion element 112 may be arranged along the second light path and between the second incoupling element 111 and the second part 112b of the second expansion element 112.

In particular, a central region of the first part 112a of the second expansion element 112 may be arranged along the first axis, Optionally, the first part 112a of the second expansion element 112 may be configured to direct the received light towards the second part 112b of the second expansion element 112 along an axis perpendicular to the first axis. For instance, the first part 112a of the second expansion element 112 may be placed at the bottom of the second incoupling element 111. The first part 112a of the second expansion element 112 may diffract the light coming from the top (i.e., from the second incoupling element 111) to the bottom and then to the left (i.e., to the second part 112b of the second expansion element 112).

FIG. 4 shows the K vector space charts of the left eye (FIG. 4a)) and right eye (FIG. 4b)) of the embodiment as shown in FIG. 3. In particular, the K vector space chart show the working principle of the waveguide A. It should be noted that the architecture for the left and right eyes can be exchanged.

It is worth mentioning that, although FIG. 2 and FIG. 3 shows two embodiments where only one of the expansion elements of the optical device 10 is divided into two parts, it is also possible to have both of the first expansion element 102 and the second expansion element 112 being divided into two parts. Such design is also covered in this disclosure.

Further, according to an embodiment of the disclosure, the optical device 10 may further comprise a retroreflector. The retroreflector may be used to reflect the light diffracted to the other direction (if there is any) back to the waveguide A.

FIG. 5 shows an optical device 10 according to an embodiment of the disclosure, which also builds on the embodiment shown in FIG. 1. Same elements in FIG. 1 and FIG. 5 share the same reference signs and function likewise. In this embodiment of the disclosure, the optical device 10 may further comprise a first retroreflector 104 and/or a second retroreflector 114.

Optionally, the first retroreflector 104 may be configured to absorb light from the first incoupling element 101 that are directed to a direction other than the first direction, and to direct it at least partly to the first incoupling element 101. Alternatively or additionally, the first retroreflector 104 may be configured to receive light from the first incoupling element 101 that are directed to a direction other than the first direction, and to direct it at least partly to the first incoupling element 101.

Optionally, the second retroreflector 114 may be configured to absorb light from the second incoupling element 111 that are directed to a direction other than the second direction, and to direct it at least partly to the second incoupling element 111. Alternatively, or additionally, the second retroreflector 114 may be configured to receive light from the second incoupling element 111 that are directed to a direction other than the second direction, and to direct it at least partly to the second incoupling element 111.

In this way, the retroreflectors, i.e., the first retroreflector 104 and/or the second retroreflector 114, may recycle or absorb the light to the undesired side, and thus may further reduce the crosstalk.

As previously described, the first portion of light 11 and/or the second portion of light 12 may be from a light generation engine 20 as shown in FIG. 1, FIG. 2, FIG. 3 or FIG. 5. FIG. 6 shows working principles of a light engine 20 according to an embodiment of the disclosure.

The light engine 20 may comprise a liquid crystal on silicon (LCOS) and an EPE. The LCOS and the EPE are the Fourier surface and image surface of the light-emitting diode (LED) light source, respectively. The light source may be separated into two parts. Notably, the light is time-sequential, and is switched for the first incoupling element 101 and the second incoupling element 111 (up and down incoupling element). In this way, the light is divided into two portions, and each portion of light may be discrete in time. It is worth mentioning that at different time point, only a part of the LED could be lit on. This means, only one of the incouplers (i.e., the first incoupling element 101 and the second incoupling element 111) works at one time instant.

FIG. 7 shows an AR device 100 according to an embodiment of the disclosure. According to embodiments of the disclosure, the AR device 100 comprises an optical device 10 and a light engine 20. In particular, the optical device 10 may be one of the optical devices as shown in FIG. 1, FIG. 2, FIG. 3 and FIG. 5. Possibly, the light engine 20 is as shown in FIG. 6.

In particular, the light engine 20 may be configured to generate a first portion of light 11 and a second portion of light 12. Accordingly, the first incoupling element 101 of the optical device 10 may receive the first portion of light 11 and may further couple the first portion of the light 11 into the waveguide A. Similarly, the second incoupling element 111 of the optical device 10 may receive the second portion of light 12 and may further couple the second portion of the light 12 into the waveguide A. As described in the previous embodiments, the light may be further coupled out of the waveguide A. Notably, the light coupled out of the waveguide A by the first outcoupling element 103 and the second outcoupling element 113 may be directed to the eyes of a user of the AR device 10.

Optionally, according to an embodiment of the disclosure, the AR device 100 may be further configured to generate light that is time-sequential. Then, the AR device 100 may be configured to divide the light into the first portion and the second portion.

FIG. 8 shows a method 800 according to an embodiment of the disclosure, which employs the optical device 10. The method 800 is for guiding light towards an AR device 100. The method 800 comprises: a step 801 of providing of an optical device 10 according to the previously described embodiments (as shown in FIG. 1, FIG. 2, FIG. 3 and FIG. 5); a step 802 of receiving a first portion of light 11 and a second portion of light 12; a step 803 of guiding the received light at least partly along a first light path and a second light path; and a step 804 of coupling the received light out of the waveguide A and towards the AR device 100. The AR device 100 may be the AR device shown in FIG. 7.

FIG. 9 shows a method 900 according to an embodiment of the disclosure, which employs the AR device 100. The AR device 100 may be the AR device shown in FIG. 7. The method 900 is for providing an AR. The method 900 comprises: a step 901 of generating a first portion of light 11 and a second portion of light 12 related to a virtual image; a step 902 of providing the generated first portion of the light 11 to the first incoupling element 101, and the generated second portion of the light 12 to the second incoupling element 111, of an optical device 10. The optical device 10 may be one of the optical devices as shown in FIG. 1, FIG. 2, FIG. 3 and FIG. 5.

The method 900 further comprises a step 903 of providing of an optical device 10 according to the previously described embodiments (as shown in FIG. 1, FIG. 2, FIG. 3 and FIG. 5). In particular, the light coupled out of the waveguide A by the first outcoupling element 103 and the second outcoupling element 113 is combined with light related to a real -world image.

The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed disclosure, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.