Optical waveguiding element, method of preparing an optical waveguide element and optical assembly

Abstract

An optical waveguiding element (10) is proposed which provides optical isolation of the waveguiding element in a stacked optical assembly. The waveguiding element comprises a first surface (12) and a second surface (14) opposite the first surface (12), an input coupling region (16) configured to couple an image light into the waveguiding element (10), and a viewing area (22) including an output coupling region (20) configured to couple the image light propagated in the optical waveguiding element (10) out of the waveguiding element (10). To provide optical isolation, at least one of the first surface (12) and the second surface (14) comprises a reflective coating (26, 26') applied in a peripheral region (24) of the at least one of the first and second surfaces (12, 14) outside the viewing area (22) and outside the input coupling region (16).

Description

Optical waveguiding element, method of preparing an optical waveguide element and optical assembly

[0001] The invention relates to an optical waveguiding element for a stacked optical assembly. The invention further relates to a corresponding method of preparing an optical waveguiding element, and still further to a corresponding optical assembly comprising an optical waveguiding element.

[0002] Smart or data eyeglasses can comprise head-mounted displays such as waveguide-based displays to project virtual images to a viewer's eye or eyes, but they also need to function as ophthalmic eyeglasses, i.e. to correct visual powers of the viewer's eyes as required by an ophthalmic prescription. For this end, head-mounted displays can comprise an ophthalmic or prescription lens (so-called Rx lens) in a stacked arrangement with a waveguide in front and / or behind the waveguide. Smart or data eyeglasses equipped with one or more ophthalmic or prescription lenses can be referred to as Rx-enabled smart or data eyeglasses.

[0003] In general, a waveguide, e.g. a planar waveguide, is designed to guide virtual image light provided by an imager through total internal reflection (TIR) to an output coupling structure where the image light is outcoupled from the waveguide towards an eye box in direction of the viewer's eye or eyes. In eyeglasses the waveguide has thereby to be placed in conditions that do not degrade TIR of light beams inside the waveguide, inbetween its reflection-intended surfaces, i.e. to optically isolate the reflection-intended surfaces of the waveguide. This can be achieved for example with a large enough change of a refractive index or reflectivity at the reflection-intended surfaces.

[0004] It is known to create an air or vacuum gap around the reflection-intended surfaces of the waveguide, i.e. around a waveguiding part of the waveguide, for enabling TIR of the image light inside the waveguiding part by arranging separating means or separators between adjacent surfaces of the waveguide and of optical components surrounding the same, e.g. an Rx lens stacked with the waveguide, for example, as it is described in US 11 243398 B2. US 11 243 398 B2 is also directed to solving the problemof a breach of TIR conditions in areas where separators overlap with the waveguiding part. This problem is common since the separators can (and usually are) be made of a material having a refractive index close to or matching a refractive index of the waveguide. WO 2024 / 008593 A1 discloses that the separating means comprise a layer of adhesive that makes a manufacture of the stacked optical assembly of a waveguide and a lens easier and cost-effective. The drawback of the latter solution is a breach of TIR at the area of the adhesive-waveguide interface. US 11 243 398 B2 solves this problem by a specific, more complex design of the separating means to be a peripheral sealing arrangement inbetween adjacent surfaces of a waveguide and a lens that has a portion exhibiting a locally reduced optical coupling as compared to the rest of the sealing arrangement to preserve TIR inside the waveguide. Said portion can comprise a mirror film as an optical isolation means deposited on the waveguide surface and a sealing-waveguide interface. Such optical isolation known from US 11 243 398 B2 seems to be effective, but its local deposition as a part of the sealing and separating arrangement makes the overall manufacture process more complex and essentially eliminates benefits of a simple adhesive separating means as disclosed in WO 2024 / 008 593 A1.

[0005] Thus, there is a need for a simple and effective technique for providing optical isolation of the adhesive-waveguide and / or separating means-waveguide interface in stacked optical assemblies, for example a stack of a waveguide and a lens.

[0006] It is an object of the present invention to provide an optical waveguiding element for a stacked optical assembly which eliminates the above-described drawbacks of the prior art at which enables optical isolation of the optical waveguiding element for a stacked optical assembly in a simple and effective technique.

[0007] It is a further object of the present invention to provide a corresponding method of preparing such an optical waveguiding element.

[0008] It is a yet further object of the present invention to provide a corresponding stacked optical assembly comprising such an optical waveguiding element and at least one further optical component.

[0009] According to a first aspect of the invention, an optical waveguiding element for a stacked optical assembly is provided, comprising a first surface and a second surface opposite the first surface, an input-coupling region configured to couple an image light into the waveguiding element, and a viewing area including an output coupling region configured to couple the image light propagated in the optical waveguide out of the waveguide, wherein at least one of the first surface and the second surface comprises a reflective coating applied in a peripheral region of the at least one of the first and second surfaces outside the viewing area and outside the input coupling region.

[0010] According to the invention, an optical waveguiding element is provided which has a reflective coating, in particular a high-reflective coating, also referred to as a mirror coating, on at least one of its first and second surfaces intended for reflection of the image light propagating in the waveguiding element, wherein the reflective coating is applied in a peripheral area of the waveguiding element, wherein the input coupling region and the viewing area including the output coupling region are not coated with the reflective coating. Differently from the prior art, the reflective coating is part of the optical waveguiding element itself, i.e. the reflective or mirror coating is not applied when a separating means is created, e.g. to provide an air gap during assembly of a stacked optical arrangement, as the mirror coating is not a part of the separating means. The mirror coating rather is applied during manufacture of the waveguide or as an extra waveguide surface treatment before the assembly of the stacked optical arrangement. As the coating is part of the optical waveguiding element itself, i.e. the mirror coating is created before and irrespectively of any assembling processes of a stacked optical arrangement it enables using much more simple and cost-effective coating techniques.

[0011] In other words, the mirror coating provides for preparing a universal, preisolated waveguiding element for a stacked optical assembly that is compatible with any techniques of assembly and any means for creating air gaps in optical arrangements.

[0012] Since the mirror coating is applied in a peripheral region of the first and / or second surfaces outside the viewing area and outside the input coupling region, it is not required to provide the reflective coating with any transparency. Further, the see- through function in the viewing region of, for example, eyeglasses is not affected by thecoating and a minor lack of transparency in the edges will either be not visible or cause insignificant discomfort to a viewer. Moreover, the mirror coating at the periphery of the waveguide will prevent unintended input coupling of any external / parasite light into the waveguide which can further decrease stray light and improve the projected virtual image quality.

[0013] In an embodiment, the reflective coating extends along the whole peripheral length of the at least one of the first and second surfaces of the waveguiding element.

[0014] This embodiment is advantageous as the mirror coating along the whole periphery of the waveguide will prevent unintended input coupling of any external / parasite light from any directions into the waveguide so that the projected virtual image quality is further improved. Furthermore, when the waveguiding element is assembled with an optical component, like a lens, bonded to the waveguiding element, and / or the optical assembly is sealed along its entire peripheral length, the reflective coating maintains TIR conditions along the entire peripheral length of the optical assembly. The same holds if a separating means (which may also be referred to as spacer structure) to provide a gap between the waveguiding element and the optical component are present in the optical assembly which extend along the entire peripheral length of the optical assembly.

[0015] In this regard, and in a further embodiment, the at least one of the first and second surfaces may comprise the reflective coating in a region of the at least one of the first and second surfaces which is designed for bonding the waveguide to another optical component of the stacked optical assembly, e.g. a lens, and / or wherein the at least one of the first and second surfaces may comprise the reflective coating in a region of the at least one of the first and second surfaces which is designed for separating the waveguide from the other optical component to provide a gap between the waveguide and the other optical component.

[0016] Bonding materials, sealing materials and / or materials of separating means typically have a refractive index which is similar to the refractive index of thematerial of the waveguiding element, which could give rise for coupling out the image light into the bonding material, sealing material and / or material of the separating means. The reflective coating of the waveguiding element according to the invention ensures avoiding light losses in these regions of the optical waveguiding element.

[0017] In a further embodiment, the first surface of the waveguiding element may comprise a first reflective coating in a peripheral region of the first surface outside the viewing area and outside the input coupling region, and a second surface of the waveguiding element may comprise a second reflective coating in a peripheral region of the second surface outside the viewing area.

[0018] This embodiment is advantageous if the optical waveguiding element is provided for a stacked optical assembly having bonded an optical component on both the first and second surfaces of the optical waveguiding element, such as a first lens bonded to the first surface of the waveguiding element and a second lens bonded to the second surface of the waveguiding element. The reflective coatings on both the first and second surfaces of the waveguiding element ensure maintaining the TIR conditions at both the first and second surfaces of the waveguiding element.

[0019] In connection with the afore-mentioned embodiment, a further embodiment provides that the first reflective coating of the first surface of the waveguiding element and a second reflective coating of the second surface of the waveguiding element may extend along the whole peripheral length of the first and second surfaces.

[0020] The advantage of this embodiment is the same as described above when a reflective coating is provided only on one of the first and second surfaces of the waveguiding element.

[0021] According to another aspect of the present invention, a method of preparing an optical waveguiding element for a stacked optical assembly is provided, comprising:providing the optical waveguiding element having a first surface and a second surface opposite the first surface, an input coupling region configured to couple an image light into the waveguiding element, and the viewing area including an output coupling region configured to couple the image light propagated in the optical waveguiding element out of the waveguiding element, applying a reflective coating on at least one of the first surface and the second surface in a peripheral region of the at least one of the first and second surfaces outside the viewing area and outside the input coupling region.

[0022] As described above, the reflective coating, especially a high-reflecting coating, also referred to as mirror coating, can be applied during a waveguide manufacture or as an extra waveguide surface treatment before the assembly of the optical waveguiding element with an optical component to form a stacked optical assembly. That is, the mirror coating is not applied when a separating means is created to provide an air gap during a stacked optical arrangement assembly as the reflective coating is not a part of the separating means. As the reflective coating is created before and irrespectively of any assembling process of a stacked optical arrangement, it enables using much more simple and cost-effective coating techniques. Moreover, the proposed mirror coating can be effectively used in combination with any techniques and means of a stacked optical arrangement assembly as well as with any techniques and means for an air gap creation and maintenance in the stacked optical arrangements, i.e. it is compatible with any types of separating means, bonding means, sealing means, either known or those that can be created in the future. As such, the proposed mirror coating provides for preparing a universal, pre-isolated waveguiding element for a stacked optical assembly that is compatible with any techniques of assembly and any means for creating air gaps in optical assemblies.

[0023] In an embodiment, said applying said reflective coating comprises applying said reflective coating along the whole peripheral length of the at least one of the first and second surfaces.

[0024] In a further embodiment, said applying said reflective coating comprises applying said reflective coating in a region of the at least one of the first and second surfaces which is designed for bonding the waveguiding element to another optical component of the stacked optical assembly, and / or wherein the reflective coating is applied in a region of the at least one of the first and second surfaces of the waveguiding element which is designed for separating the waveguiding element from the other optical component to provide a gap between the waveguiding element and the other optical component.

[0025] In a further embodiment, said applying said reflective coating may comprise applying a first reflective coating on the first surface of the waveguiding element in a peripheral region of the first surface outside the viewing area and outside the input coupling region, and applying a second reflective coating on the second surface of the waveguiding element in a peripheral region of the second surface outside the viewing area.

[0026] In the context of the previous embodiment, and in a further embodiment, said applying said reflective coating may comprise applying said first reflective coating along the whole peripheral length of the first surface of the waveguiding element and applying said second reflective coating along the whole peripheral length of the second surface of the waveguiding element.

[0027] The afore-described embodiments of the method according to the invention have the same advantages as the corresponding embodiments of the waveguiding element according to the invention.

[0028] In a yet further aspect of the present invention, a stacked optical assembly is provided, comprising an optical waveguiding element according to the first aspect and at least one optical component, wherein the at least one optical component is connected, directly or through a layer of adhesive, to the at least one of the first and second surfaces of the waveguiding element in the peripheral region having the reflective coating.

[0029] In an embodiment of the stacked optical assembly according to the invention, the optical assembly may comprise a gap between the optical component and the at least one of the first and second surfaces of the waveguiding element within the viewing area.

[0030] The gap may be filled with natural air, however it could also be filled with any gaseous fluid different from natural air. The pressure in the air gap can be very low in a way that can be considered as a vacuum gap as well. In another embodiment, the air gap can be filled with a low index material ensuring the condition of total internal reflection is provided by an air or vacuum gap, wherein the low index material can have some adhesive properties by itself, but does not have to.

[0031] In a further embodiment of the stacked optical assembly according to the invention, the optical component may be connected to the first surface of the waveguiding element, and the optical assembly may further comprise a further optical component connected, directly or through a layer of adhesive, to the second surface of the waveguiding element in the peripheral region having the reflective coating.

[0032] In the context of the previous embodiment, in a further embodiment the stacked optical assembly may comprise a gap between the further optical component and the second surface of the waveguiding element within the viewing area.

[0033] In a further embodiment of the stacked optical assembly according to the invention, the at least one optical component may be a lens, such as a prescription lens (Rx lens). The further optical component, if provided, may also be an Rx lens.

[0034] It would be appreciated by those skilled in the art that the stacked optical assembly according to the invention may have the corresponding embodiments and provide the same advantages as described above with respect to the waveguiding element according to the invention.

[0035] Further features and advantages of the invention will become apparent from the following description and the accompanying drawings.

[0036] Embodiments of the invention are shown in the drawings and will be described below with reference to the drawings. In the drawings:Fig. 1 shows schematically a top plan view of a surface of an optical waveguiding element for a stacked optical assembly according to an embodiment of the present invention;Fig. 2 shows schematically the top plan view of a surface of an optical waveguiding element for a stacked optical assembly according to another embodiment of the present invention;Fig. 3 shows schematically a cross-section of an optical assembly according to an embodiment of the present invention which comprises an optical waveguiding element according to an embodiment of the present invention;Fig. 4 shows an enlarged view of a portion A of the optical assembly in Fig. 3;Fig. 5A shows schematically a cross section of an optical waveguiding element according to an embodiment to explain a method of preparing the optical waveguide for a stacked optical assembly;Fig. 5B shows schematically a stage of producing the stacked optical assembly comprising the optical waveguiding element of Fig. 5A;Fig. 5C shows schematically a further stage of producing the stacked optical assembly comprising the optical waveguiding element of Fig. 5A; andFig. 5D shows a final stage of producing a stacked optical arrangement comprising the optical waveguiding element of Fig. 5A.

[0037] Fig. 1 shows schematically a top plan view of an optical waveguiding element labeled with reference numeral 10 according to an embodiment of the present invention. The optical waveguiding element 10 is designed for a stacked optical assembly as will be described below with reference to Figs. 3 to 5. A stacked optical assembly comprising the optical waveguiding element 10 may be used in a head-mounted display, e.g. in data glasses. As such and shown in Fig. 1 , the optical waveguiding element may have a contour or shape of an eyeglass.

[0038] With additional reference to Figs. 3 and 4, the optical waveguiding element has a first surface 12 and an opposite second surface 14. Both the surfaces 12 and 14 may be planar surfaces.

[0039] The optical waveguiding element 12 further comprises an input coupling region 16 which is configured to couple an image light (not shown) into the waveguiding element 10. The image light may be emitted by a display (not shown). Image light coupled into the optical waveguiding element 10 via the input coupling region 16 propagates in the optical waveguiding element 10 along a waveguiding region 18 to an outcoupling region 20 which is designed to couple the light propagated in the optical waveguiding element 10 out of the waveguiding element 10 in an eyebox direction to project the image to the user's eye. Within the waveguiding region 18, the image light propagates via total internal reflection (TIR) at interfaces of the waveguiding element 10 to surroundings, e.g. to air. These interfaces are provided by the surfaces 12 and 14 of the optical waveguiding element 10.

[0040] The output coupling region 20 is included in a viewing area 22 of the optical waveguiding element 10. The optical waveguiding element 10 is transparent in the viewing area 22, i.e. a user can see the real world surroundings in front of the optical waveguiding element 10 through the optical waveguide 10. Thus, the optical waveguidingelement 10 is suitable for a head-mounted display of an augmented reality head-mounted device.

[0041] In an exemplarily shown peripheral region 24 of the waveguiding element 10, the optical waveguiding element 10 comprises a reflective coating, in particular a high- reflective coating 26 which is also referred to as mirror coating. The reflective coating 26 is illustrated in Fig. 1 by a hatching. The reflective coating 26 is provided in the peripheral region 24 of the surface 12 of the waveguiding element 10, but is not provided in the viewing area 22 which is surrounded by the peripheral region 24, and is also not provided in the input coupling region 16.

[0042] The region where the reflective coating is applied on the surface 12 of the optical waveguiding element 10 especially is a region where TIR conditions may be disturbed by for example a bonding material like an adhesive used for bonding the optical waveguiding element 10 to an optical component like a lens (as shown in Figs. 3 and 4), or by separating means designed for separating the optical waveguiding element 10 from an optical component bonded to the optical waveguiding element 10 to provide a gap between the optical waveguiding element 10 and the optical component (as shown in Figs. 3 and 4), and / or by a sealing material to seal the stacked optical arrangement comprising the optical waveguiding element 10 and an optical component.

[0043] Fig. 2 shows schematically a top plan view of an optical waveguiding element 10 according to another embodiment of the present invention which is a modification of the embodiment of Fig. 1. While in the embodiment of Fig. 1 the reflective coating 26 in the peripheral region 24 extends along the whole peripheral length of the surface 12, the reflective coating 26 of the optical waveguiding element 10 in the embodiment of Fig. 2 which is again illustrated by a hatching, extends in the peripheral region 24 only over a part of the peripheral length of the optical waveguiding element 10. The portion of the peripheral region 24 of the optical waveguiding element 10 in the embodiment of Fig. 2 is a part of the waveguiding region 18 where TIR conditions may be disturbed by for example a bonding material like an adhesive used for connecting the optical waveguiding element 10 to an optical component like a lens (as shown in Figs. 3 and 4), or by separating means designed for separating the optical waveguiding element 10 from an opticalcomponent bonded to the optical waveguiding element 10 to provide a gap between the optical waveguiding element 10 and the optical component (as shown in Figs. 3 and 4), and / or by a sealing material to seal the stacked optical arrangement comprising the optical waveguiding element 10 and an optical component.

[0044] Fig. 3 shows schematically an embodiment of an optical assembly 50 in a cross-section. Fig. 4 shows an enlarged view of a portion A in Fig. 3. Elements of the optical assembly 50 in Figs. 3 and 4, which are identical, comparable or similar to elements in the embodiments of Figs. 1 and 2, are denoted with the same reference numerals as in Figs. 1 and 2.

[0045] The optical arrangement 50 comprises an optical waveguiding element 10 like the optical waveguiding element 10 having a first surface 12 and a second surface 14 as described above. The optical arrangement 50 further comprises a first optical component 30 and a second optical component 32. The optical component 30 is connected to the first surface 12 of the waveguiding element 10, and the second optical component 32 is connected to the second surface 14 of the optical waveguiding element 10. Both optical components 30 and 32 may be configured as prescription lenses (Rx lenses), i.e. the optical components 30 and 32 have an optical power in accordance with a user's prescription. The optical component 30 may be a so-called push lens, and the optical component 32 may be a so-called pull lens. A pull lens serves to correct visual power of the viewer's eye as required by an ophthalmic prescription for aberrations of the image transferred by the optical waveguiding element 10 seen by the user as a virtual image. A push lens serves for correcting visual powers of the viewer's eye as required by an ophthalmic prescription for aberrations of an image of an object in the real world seen by the user through the optical arrangement 50. In the present embodiment, the push lens 30 in combination with the pull lens 32 corrects the image of an object in the real world seen by the user through the optical arrangement 50.

[0046] It is to be understood that the optical arrangement 50 may, in other embodiments of the present invention, comprise only the optical component 30 or only the optical component 32.

[0047] The optical arrangement 50 comprises a bonding structure 34 for bonding the optical component 30 to the optical waveguiding element 10. The bonding structure 34 may be an adhesive. The optical arrangement 50 further comprises a separating structure 36 to provide a gap 35 between the optical component 30 and the optical waveguiding element 10. The gap 35 maintains TIR conditions for the image light propagating in the optical waveguiding element 10 in the viewing area 22. In the present embodiment, the separating structure 36 is monolithically formed with the optical component 30, e.g. formed during molding of the component 30. In other embodiments, the separating structure 36 may be created as a part separate from the component 30.

[0048] One of or both the bonding structure 34 and the separating structure 36 may also serve as a sealing structure to seal the stacked optical assembly 50 against the surroundings.

[0049] The optical waveguiding element 10 is provided with a reflective coating 26 in a peripheral region of the optical waveguiding element 10, wherein the reflective coating 26 is provided in the region of the bonding structure 34 and in the region of the separating structure 36. The reflective coating 26 is applied on the surface 12 of the waveguiding element 10. According to the teachings of the present invention, the reflective coating 26 has been applied onto the surface 12 before assembly of the optical waveguiding element 10 with the optical component 32. The reflective coating 26 may be applied onto the optical waveguiding element 10 during manufacturing of the optical waveguiding element 10 or as an extra surface treatment just before the assembly of the stacked arrangement of the optical component 30 and the optical waveguiding element 10.

[0050] The reflective coating 26 is provided in the peripheral region of the optical waveguiding element 10 outside the viewing region 22 of the optical waveguiding element 10 as described above. Depending on whether the image light from the display (not shown) enters the input coupling region 16 through the first surface 12 or through the second surface 14 of the optical waveguiding element 10, the opposite surface is preferably coated with the reflective coating 26. That is, when the image light enters the inputcoupling region 16 through the surface 12, the surface 14 may be coated with the reflective coating, and vice versa.

[0051] A similar bonding structure 34' and a similar separating structure 36' is provided in the optical arrangement 50 between the optical component 32 and the optical waveguiding element 10, wherein reference is made to the description above of the bonding structure 34, the separating structure 36 and the gap 35. Corresponding elements are denoted with reference numerals supplemented with a prime. Accordingly, the optical waveguiding element 10 comprises a reflective coating 26' on the surface 14 in the peripheral region of the surface 14 of the waveguiding element 10, wherein reference is made to the description of the reflective coating 26 on the surface 12 above.

[0052] The reflective coatings 26 and 26' may extend over the whole peripheral length of the first surface 12 and the second surface 14, respectively.

[0053] In the following, an embodiment of preparing an optical waveguiding element, like waveguiding element 10 in Figs. 1-4, for a stacked optical assembly, like stacked optical assembly 50, and the assembling of the optical stack after preparation of the optical waveguiding element 10 will be described in the following.

[0054] According to an embodiment of the method of preparing an optical waveguiding element, the optical waveguiding element 10 is provided having a first surface 12 and a second surface 14 opposite the first surface 12, an input coupling region 16 (Fig. 1) configured to couple an image light into the waveguiding element 10, and a viewing area 22 (Fig. 1) including an output coupling region 20 (Fig. 1) configured to couple the image light propagated in the optical waveguiding element 10 out of the waveguiding element 10. The method of preparing the optical waveguiding element 10 comprises applying a reflective coating 26 on at least one of the first and second surfaces 12, 14, in the present embodiment on the surface 12 of the optical waveguiding element 10. The reflective coating is applied in a peripheral region 24 of the surface 12 of the waveguiding element 10 outside the viewing area 22 and outside the input coupling region 16 (as shown in Fig. 1 and 2). Applying the reflective coating may comprise depositing ametal layer, e.g. a silver layer, onto the surface 12 of the waveguiding element 10 in a peripheral region thereof.

[0055] Applying the reflecting coating 26 may be part of a surface treatment of the optical waveguiding element 10, before depositing a layer of material, e.g. an adhesive, to create the bonding and / or separating and / or sealing structure of the optical arrangement 10. The reflective coating 26 provides an optical isolation of the interface between the optical waveguiding element 10 and the bonding structure and / or separating structure and / or sealing structure. In other embodiments, the optical waveguiding element 10 may be provided with the reflective coating 26 already during manufacturing of the optical waveguiding element 10.

[0056] With the optical waveguiding element 10 prepared in this way, assembling of the stacked optical arrangement 50 can be performed. Fig. 5B shows an embodiment of an assembling procedure, where a separating structure 48, a bonding structure 44 and a sealing structure 46 have been applied onto the surface of the reflective coating 26. The sealing structure 46 may be omitted, if the sealing function is accomplished by the bonding and / or separating structures 44, 48.

[0057] The structures 44, 46 and 48 may be applied onto the surface of the reflective coating 26 according to any suitable manner, for example by applying these structures in liquid form, for example as a liquid adhesive, onto the surface of the reflective coating 26.

[0058] Next, as shown in Fig. 5C, an optical component, like optical component 30 in Fig. 3, is provided as part of the optical arrangement 50. The optical component 30 is joined to the optical waveguiding element 10 by applying a joining force 47, which may be the force of gravity only, onto the optical component 30 so that the optical component 30 is bonded to the optical waveguiding element 10, as shown in Fig. 5D. The separating structure 48 provides for a gap 35 between the optical component 30 and the optical waveguiding element 10.

[0059] In case of the embodiment of Figs. 3 and 4, according to which the optical arrangement 50 additionally comprises the optical component 30 bonded to the surface 12 of the optical waveguiding element 10, the optical waveguiding element 10 is prepared with an additional reflective coating 26 like reflective coating 26' on the surface 14 in the peripheral region thereof.

[0060] As follows from the above description, the proposed mirror coating 26, 26' is a universal, cost-effective solution being fully compatible with a series production that provides for optical isolation of a waveguiding element 10 in stacked optical assemblies to increase a projected virtual image quality.

Claims

Claims1. Optical waveguiding element (10) for a stacked optical assembly, comprising a first surface (12) and a second surface (14) opposite the first surface (12), an input coupling region (16) configured to couple an image light into the waveguiding element (10), and a viewing area (22) including an output coupling region (20) configured to couple the image light propagated in the optical waveguiding element (10) out of the waveguiding element (10), wherein at least one of the first surface (12) and the second surface (14) comprises a reflective coating (26, 26’) applied in a peripheral region (24) of the at least one of the first and second surfaces (12, 14) outside the viewing area (22) and outside the input coupling region (16).

2. Optical waveguiding element of claim 1, wherein the reflective coating (26, 26’) extends along the whole peripheral length of the at least one of the first and second surfaces (12, 14) of the waveguiding element (12, 14).

3. Optical waveguiding element of claim 1 or 2, wherein the at least one of the first and second surfaces (12, 14) comprises the reflective coating (26, 26’) in a region of the at least one of the first and second surfaces (12, 14) which is designed for bonding the waveguiding element (10) to another optical component (30, 32) of the stacked optical assembly, and / or wherein the at least one of the first and second surfaces (12, 14) comprises the reflective coating (26, 26’) in a region of the at least one of the first and second surfaces (12, 14) of the waveguiding element (10) which is designed for separating the waveguiding element (10) from the other optical component (30, 32) to provide a gap (35, 35’) between the waveguiding element (10) and the other optical component (30, 32).

4. Optical waveguiding element of any one of claims 1 to 3, wherein the first surface (12) of the waveguiding element (10) comprises a first reflective coating (26) in a peripheral region (24) of the first surface (12) outside the viewing area (22) and outside the input coupling region (16), and the second surface (14) of thewaveguiding element (10) comprises a second reflective coating (26’) in a peripheral region (24) of the second surface (14) outside the viewing area (22).

5. Optical waveguiding element of claim 4, wherein the first reflective coating (26) of the first surface (12) of the waveguiding element (10) and the second reflective coating (26’) of the second surface (14) of the waveguiding element (10) extend along the whole peripheral length of the first and second surfaces (12, 14).

6. Method of preparing an optical waveguiding element (10) for a stacked optical assembly, comprising: providing the optical waveguiding element (10) having a first surface (12) and a second surface (14) opposite the first surface (12), an input coupling region (16) configured to couple an image light into the waveguiding element (10), and a viewing area (22) including an output coupling region (20) configured to couple the image light propagated in the optical waveguiding element (10) out of the waveguiding element (10), applying a reflective coating (26, 26’) on at least one of the first surface (12) and the second surface (14) in a peripheral region (24) of the at least one of the first and second surfaces (12, 14) outside the viewing area (22) and outside the input coupling region (16).

7. Method of claim 6, wherein said applying said reflective coating (26, 26’) comprises applying said reflective coating (26, 26’) along the whole peripheral length of the at least one of the first and second surfaces (12, 14).

8. Method of claim 6 or 7, wherein said applying said reflective coating (26, 26’) comprises applying said reflective coating (26, 26’) in a region of the at least one of the first and second surfaces (12, 14) of the waveguiding element (10) which is designed for bonding the waveguiding element (10) to another optical component (30, 32) of the stacked optical assembly, and / or wherein the reflective coating (26,26’) is applied in a region of the at least one of the first and second surfaces (12, 14) of the waveguiding element (10) which is designed for separating the waveguiding element (10) from the other optical component (30, 32) to provide a gap (35, 35’) between the waveguiding element (10) and the other optical component (30, 32).

9. Method of any one of claims 6 to 8, wherein said applying said reflective coating (26, 26’) comprises applying a first reflective coating (26) on the first surface (12) of the waveguiding element (10) in a peripheral region (24) of the first surface (12) outside the viewing area (22) and outside the input coupling region (16), and applying a second reflective coating (26’) on the second surface (14) of the waveguiding element (10) in a peripheral region (24) of the second surface (14) outside the viewing area (22).

10. Method of claim 9, wherein said applying said reflective coating (26, 26’) comprises applying said first reflective coating (26) along the whole peripheral length of the first surface (12) of the waveguiding element (10) and applying said second reflective coating (26’) along the whole peripheral length of the second surface (14) of the waveguiding element (10).

11. Stacked optical assembly, comprising an optical waveguiding element (10) according to any one of claims 1 to 5 and at least one optical component (30, 32), wherein the at least one optical component (30, 32) is connected, directly or through a layer of adhesive, to the at least one of the first and second surfaces (12, 14) of the waveguiding element (10) in the peripheral region (24) having the reflective coating (26, 26’).

12. Stacked optical assembly of claim 11, comprising a gap (35, 35’) between the optical component (30) and the at least one of the first and second surfaces (12, 14) of the waveguiding element (10) in the viewing area (22).

13. Stacked optical assembly of claim 11 or 12, wherein the optical component (30) is connected to the first surface (12) of the waveguiding element (10), and the optical assembly (50) further comprises a further optical component (32) connected, directly or through a layer of adhesive, to the second surface (14) of the waveguiding element (10) in the peripheral region (24) having the reflective coating.

14. Stacked optical assembly of claim 13, comprising a gap (35’) between the further optical component (32) and the second surface (14) of the waveguiding element (10) in the viewing area (22).

15. Stacked optical assembly of any one of claims 11 to 14, wherein the at least one optical component (30, 32) is a lens.

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