Beam splitter, stack comprising two or more such beam splitters and method of manufacturing such a beam splitter

Abstract

The invention relates to a beam splitter and a method for manufacturing such a beam splitter. The invention also relates to a stack comprising two or more such beam splitters.

Description

Technical Field

[0001] The invention relates to a beam splitter and a method for manufacturing such a beam splitter. The invention also relates to a stack comprising two or more such beam splitters. Background Art

[0002] In a reflective augmented reality waveguide, light from a projector coupled into the waveguide is directed, altered, or reflected from within the waveguide with the aid of one or more beam splitters and into the user's eyes. However, when using conventional waveguides, the image quality presented to the user is often poor due to low contrast, insufficient color fidelity, and reduced clarity.

[0003] It is therefore an object of the present invention to overcome the above mentioned drawbacks and to provide means for improving the quality of the respective images presented to the user. Summary of the invention

[0004] According to a first aspect, the present invention solves this problem by proposing a beam splitter.

[0005] In particular, the problem is solved by a beam splitter comprising a substrate made of a substrate material and at least one coating arranged on at least one main surface of the substrate, wherein the substrate and all coatings have a total thickness along a first direction parallel to a normal vector of the main surface, and

[0006] where, for a particular light beam with a particular chromaticity defined by CIE x and y,

[0007] The specific light beam is incident on the beam splitter along a second direction at at least one incident angle sandwiched between a vector pointing in the first direction and a vector pointing in the second direction, and the incident angle is in the range of 15° to 75°, preferably in the range of 15° to 45°, particularly preferably in the range of 20° to 42°, and particularly preferably at an angle of 32°.

[0008] and the specific light beam is partially transmitted through the beam splitter and partially reflected by the beam splitter,

[0009] the difference between the CIE x-coordinate of the particular beam after transmission through the beam splitter and the CIE x-coordinate of the beam after transmission through the beam splitter is less than 0.05, preferably less than 0.025, and more preferably less than 0.005, and / or

[0010] The difference between the CIE y coordinate of the particular beam after transmission through the beam splitter and the CIE y coordinate of the beam after transmission through the beam splitter is less than 0.05, preferably less than 0.025, and more preferably less than 0.005.

[0011] Thus, it was surprisingly found that when a corresponding beam splitter is used in a reflective augmented reality waveguide, controlling the color shift of the transmitted beam and optionally the reflected beam can significantly improve the image quality. It was also found that in some embodiments, when a corresponding beam splitter is used in a reflective augmented reality waveguide, additionally controlling the phase of the transmitted beam can significantly improve the image quality.

[0012] The inventors believe that if the color shift and preferably the phase difference of the light beam transmitted through the beam splitter is controlled as described, the slight differences in the propagation paths of the multiple light beams emitted by the projector for different colors and / or different pixels of the image to be presented and which light beams mix in the user's eye are no longer so important.

[0013] Therefore, if a corresponding color shift is set for a corresponding incident angle in the range of 15° to 75°, preferably 15° to 45°, preferably 20° to 42°, and in particular at an angle of 32°, and for a corresponding specific wavelength of a specific light beam in the range of 400 to 730nm, preferably 420nm to 680nm, more preferably 430nm to 650nm, and particularly preferably 450nm to 650nm, the beam splitter can be used to provide high-quality images to the user.

[0014] In addition, preferably, when used in an AR (augmented reality) device, such as AR glasses, the structure of the beam splitter does not substantially affect the appearance of the user's eyes in the eyes of a third person. Generally speaking, in the direction of the line of sight between the user's eyes and the third person, the appearance of the user's eyes in the eyes of the third person may be affected by the anti-reflection effect of the coating. Therefore, preferably, within the angle range in which the AR photo is guided, the reflectivity is higher than the angle range in which the user looks to the outside world through the beam splitter. For example, the main propagation direction of light, in particular the transmitted part of the light (such as a specific light beam), in the beam splitter can be selected to be different directions, in particular perpendicular to the direction of the line of sight between the user's eyes and the third person.

[0015] Preferably, it will be clear to those skilled in the art that the difference between the CIE x-coordinate and the corresponding y-coordinate of a particular light beam and the CIE x-coordinate and the corresponding y-coordinate of the particular light beam after transmission through the beam splitter is evaluated by measuring (1) the CIE x-coordinate and the y-coordinate of the light beam incident on the beam splitter and (2) the CIE x-coordinate and the y-coordinate of the light beam transmitted through the beam splitter. It will also be clear to those skilled in the art that the difference between the CIE x-coordinate and the corresponding y-coordinate of a particular light beam and the CIE x-coordinate and the corresponding y-coordinate of the reflected light beam is evaluated by measuring (1) the CIE x-coordinate and the y-coordinate of the light beam incident on the beam splitter and (2) the CIE x-coordinate and the y-coordinate of the reflected light beam.

[0016] For the purposes of the present invention, "color shift" refers to the difference in the CIE x, y coordinates of a particular light beam from the transmitted and reflected (partial) light beams, respectively.

[0017] For the purposes of the present invention, the transmitted part of the light beam is also referred to as a "transmitted light beam" or a "transmitted partial light beam", and the reflected part of the light beam is also referred to as a "reflected light beam" or a "reflected partial light beam".

[0018] The color shift can be obtained by performing spectrophotometric measurements on a specific light beam and a corresponding reflected and / or transmitted light beam, converting the obtained measurement data into CIE color coordinates according to a CIE standard observer function, and calculating the difference between the CIE color coordinates of the specific light beam and the corresponding reflected and / or transmitted light beam.

[0019] Preferably, the specific light beam is incident on the beam splitter at a first surface of the beam splitter, such as a first main surface of the beam splitter.In particular, the first surface of the beam splitter is an outer surface of the coating.

[0020] Preferably, for evaluating the color shift, the transmitted portion of the specific beam at the second surface of the beam splitter, such as the second main surface of the beam splitter, is used. In particular, the second surface of the beam splitter is an outer surface of the beam splitter facing in the opposite direction compared to the outer surface of the coating.

[0021] According to the present invention, after the specific light beam is transmitted through the beam splitter, the difference between the CIE x coordinate of the specific light beam and the CIE x coordinate of the specific light beam after being transmitted through the beam splitter is less than 0.05, preferably less than 0.025, more preferably less than 0.005; and / or the difference between the CIE y coordinate of the specific light beam and the CIE y coordinate of the specific light beam after being transmitted through the beam splitter is less than 0.05, preferably less than 0.025, more preferably less than 0.005.

[0022] Preferably, the chromaticity x according to the CIE standard of the specific light beam incident on the beam splitter is in the range of 0.283 to 0.383, preferably in the range of 0.300 and 0.360, more preferably in the range of 0.310 and 0.350, and particularly preferably in the range of 0.320 to 0.340; and / or the chromaticity y according to the CIE standard of the specific light beam incident on the beam splitter is in the range of 0.283 to 0.383, preferably in the range of 0.300 to 0.360, more preferably in the range of 0.310 and 0.350, and particularly preferably in the range of 0.320 to 0.340.

[0023] Preferably, the x chromaticity of the transmitted partial light beam according to the CIE standard is in the range of 0.283 to 0.383, preferably in the range of 0.300 and 0.360, more preferably in the range of 0.310 and 0.350, and particularly preferably in the range of 0.320 to 0.340; and / or the y chromaticity of the transmitted partial light beam according to the CIE standard is in the range of 0.283 to 0.383, preferably in the range of 0.300 and 0.360, more preferably in the range of 0.310 and 0.350, and particularly preferably in the range of 0.320 to 0.340.

[0024] Preferably, the beam splitter is designed so that the beam according to the specific beam is partially reflected by the beam splitter and partially transmitted through the beam splitter.Thus, the specific beam incident on the beam splitter is split into at least two partial beams.

[0025] The specific light beam incident on the beam splitter, the reflected light beam and the transmitted light beam preferably propagate in a common propagation plane. In particular, the angle between the first direction and the second direction is measured in the common propagation plane.

[0026] Preferably, for the reflected light beam, the difference between the CIE x-coordinate of the specific light beam and the CIE x-coordinate of the reflected light beam is less than 0.05, preferably less than 0.025, more preferably less than 0.005; and / or the difference between the CIE y-coordinate of the specific light beam and the CIE y-coordinate of the reflected light beam is less than 0.05, preferably less than 0.025, more preferably less than 0.005.

[0027] Preferably, the x chromaticity of the reflected light beam according to the CIE standard is in the range of 0.283 to 0.383, preferably in the range of 0.300 and 0.360, more preferably in the range of 0.310 and 0.350, and particularly preferably in the range of 0.320 to 0.340; and / or the y chromaticity of the reflected light beam according to the CIE standard is in the range of 0.283 to 0.383, preferably in the range of 0.300 and 0.360, more preferably in the range of 0.310 and 0.350, and particularly preferably in the range of 0.320 to 0.340.

[0028] Optionally, the maximum color shift criterion is met for a beam splitter having a temperature between 0°C and 60°C, such as 20°C (e.g. the ambient temperature may be within this range). In other words, the color shift of the beam splitter is preferably evaluated when its temperature is within said temperature range. Thus, it is possible that for a certain incident angle, e.g. 30° or 32°, and a certain wavelength of the beam, the evaluated color shift is above 0.05 for x and above 0.05 for y according to the CIE standard if the temperature of the beam splitter is outside said range.

[0029] In one embodiment, the color shift meets a maximum color shift criterion for each specific wavelength in the range. In other words, the quality factor applies not only to (at least) one single wavelength selected to meet the specific wavelength, but to each wavelength in the range.

[0030] Preferably, the beam splitter according to the invention has a wavelength-dependent transmittance and a wavelength-dependent reflectivity,

[0031] wherein, for at least one specific angle of incidence, preferably for all angles of incidence in the range of 15° to 60°, preferably in the range of 15° to 45° and / or in the range of 20° to 42°, and / or at angles of incidence of 30° and / or 60°,

[0032] In the wavelength range of 420nm to 680nm, the beam splitter has a maximum transmittance T (420-680)最大 and minimum transmittance T (420-680)最小 , where T (420-680)最大 and T (420-680)最小 The difference is less than 10%, preferably less than 7%, more preferably less than 5%, particularly preferably less than 3%, and / or

[0033] The beam splitter has a maximum reflectivity R in the wavelength range of 420nm to 680nm. (420-680)最大 and minimum reflectivity R (420-680)最小 , where R (420-680)最大 and R (420-680)最小 The difference is less than 10%, preferably less than 7%, more preferably less than 5%, particularly preferably less than 3%, and / or

[0034] At a wavelength of 430nm, the beam splitter has a maximum transmittance T (430)最大 and minimum transmittance T (430)最小 , where the maximum transmittance T (430)最大 and minimum transmittance T (430)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or

[0035] At a wavelength of 430 nm, the beam splitter has a maximum reflectivity R (430)最大 and minimum reflectivity R (430)最小 , where R (430)最大 and R (430)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or

[0036] At a wavelength of 535 nm, the beam splitter has a maximum transmittance T (535)最大 and minimum transmittance T (535)最小 , where T (535)最大 and T (535)最小The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or

[0037] At a wavelength of 535nm, the beam splitter has a maximum reflectivity R (535)最大 and minimum reflectivity R (535)最小 , where R (535)最大 and R (535)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or

[0038] At a wavelength of 565nm, the beam splitter has a maximum transmittance T (565)最大 and minimum transmittance T (565)最小 , where T (565)最大 and T (565)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or

[0039] At a wavelength of 565nm, the beam splitter has a maximum reflectivity R (565)最大 and minimum reflectivity R (565)最小 , where R (565)最大 and R (565)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, and particularly preferably less than 2%.

[0040] In a preferred embodiment, the invention relates to a beam splitter according to the invention,

[0041] Among them, for light with a specific wavelength within the range of 450nm and 650nm,

[0042] The light is incident on the beam splitter along the second direction at an incident angle of 30° sandwiched between the vector pointing to the first direction and the vector pointing to the second direction. After passing through the beam splitter, the absolute value of the phase difference of the specific light beam is less than or equal to 30° compared with the case where the beam splitter is replaced by a reference substrate made of substrate material and having a thickness the same as the total thickness of the beam splitter under the same other conditions.

[0043] In some preferred embodiments of the beam splitter according to the present invention, the absolute value of the phase difference is less than or equal to 20°, less than or equal to 15°, less than or equal to 10°, less than or equal to 7°, less than or equal to 5°, less than or equal to 3°, or less than or equal to 1°; and / or greater than or equal to 0.5°, greater than or equal to 1°, greater than or equal to 2°, or greater than or equal to 5°.

[0044] Preferably, as will be apparent to one skilled in the art, the phase difference is evaluated between (1) a specific light beam transmitted through the beam splitter and (2) a specific light beam transmitted through a reference substrate, other conditions being equal, wherein the thickness of the reference substrate corresponds to the total thickness of the beam splitter.

[0045] Preferably, the specific light beam is incident on the beam splitter at a first surface of the beam splitter, such as a first main surface of the beam splitter. In particular, the first surface of the beam splitter is an outer surface of the coating. Preferably, for evaluating the phase difference, a transmitted portion of the specific light beam at a second surface of the beam splitter, such as a second main surface of the beam splitter, is used. In particular, the second surface of the beam splitter is an outer surface of the beam splitter facing in the opposite direction compared to the outer surface of the coating.

[0046] Likewise, for the reference substrate, the specific light beam is incident on the reference substrate at a first surface of the reference substrate (such as a first main surface of the reference substrate). In particular, the first surface of the reference substrate is an outer surface and / or a main surface of the reference substrate. Preferably, in order to evaluate the phase difference, a transmitted portion of the specific light beam at a second surface of the reference substrate (such as a second main surface of the reference substrate) is used. In particular, the second surface of the reference substrate is an outer surface and / or a main surface of the reference substrate facing in an opposite direction compared to the outer surface of the reference substrate.

[0047] The term "variable X is between Y and Z" as used in this application preferably means that variable X can take any value between Y and Z (including Y and Z). For example, variable X can take value Y, value Z or any value in between.

[0048] The particular light beam preferably impinges on the beam splitter at a coupling point, which is preferably located within the first main surface of the beam splitter, and / or leaves the beam splitter at an exit point, which is preferably located within the second main surface of the beam splitter.

[0049] In some preferred embodiments, after a specific light beam is transmitted through the beam splitter, the absolute value of the phase difference thereof is less than or equal to 30° compared with the case where the beam splitter is replaced by a reference substrate made of a substrate material and having a thickness equal to the total thickness of the beam splitter under the same other conditions.

[0050] The phase difference can be measured using optical analysis. In the optical analysis, for a specific light beam propagating in an incident medium (which is preferably provided with the aid of a coupling element and / or in the form of a coupling element), a specific angle (i.e., an angle of incidence) in the range of 15° to 45°, preferably 20° to 42°, particularly preferably 30°, sandwiched between the first direction and the second direction can be measured, and the incident medium is made of the same material as the substrate. Preferably, the incident medium is attached to the beam splitter directly or indirectly (e.g., via an adhesive layer). The incident medium can be in the form of a prism, for example. Preferably, the second direction is the direction of the propagation path of the specific light beam in the coupling element.

[0051] Preferably, the reference wavefront for the phase difference is the wavefront propagating from the coupling element.

[0052] It has been shown that, in principle, for higher angles of incidence, higher phase differences can be accepted and still a high quality image can be obtained. Of course, when the beam splitter is in use, it is preferred that the beam splitter can be used over a larger range of angles of incidence. However, if, for said angle of incidence, the phase difference meets a maximum threshold criterion, such a beam splitter has been shown to be very preferred.

[0053] Preferably, the maximum threshold criterion is met for angles of incidence between 3° and 80°, in particular between 10° and 70°, in particular between 10° and 50°, or between 10° and 40°, or between 55° and 75°, or between 45° and 75°, or between 15° and 45°, or between 20° and 40°.

[0054] Preferably, the first direction is also parallel to a normal vector to a main surface of the beam splitter. The angle of incidence is therefore preferably expressed relative to this normal vector.

[0055] The relationship between the incident angle, the specific wavelength of a specific light beam and the maximum phase difference allowed by the phase difference can preferably define a quality factor. Therefore, in one embodiment, the beam splitter meets the maximum phase difference criterion for a specific light beam (which is incident at the incident angle and whose wavelength meets the specific wavelength).

[0056] For example, the substrate is made of glass ceramics, glass, optical ceramics, optical polymers and / or ceramics. In one embodiment, the substrate is made of a transparent material, which is at least transparent to wavelengths and / or specific wavelengths within the range of 400nm and 730nm, preferably within the range of 450nm and 650nm.

[0057] The beam splitter is designed so that the beam according to the specific beam is partially reflected by the beam splitter and partially transmitted through the beam splitter. Therefore, the specific beam incident on the beam splitter is divided into at least two partial beams, also called "transmitted beam" and "reflected beam".

[0058] The specific light beam incident on the beam splitter, the reflected light beam and the transmitted light beam preferably propagate in a common propagation plane. In particular, the angle between the first direction and the second direction is measured in the common propagation plane.

[0059] In one embodiment, the phase difference meets a maximum threshold criterion for each specific wavelength in the range. In other words, the quality factor applies not only to (at least) one single wavelength selected to meet the specific wavelength, but to each wavelength in the range.

[0060] As an alternative to optical analysis of phase difference, the composition of the substrate material and any coatings on a given beam splitter can be analyzed using ToF-SIMS and / or FIB-SIMS. The thickness of the substrate and coatings can be determined by electron microscopy. Finally, the phase difference can be calculated based on the refractive index of the coating and substrate materials.

[0061] The material and thickness of the coating are determined by analytical methods such as ToF-SIMS and / or FIB-SIMS. The refractive index information can be obtained experimentally or from existing databases. Based on this information, the optical properties of the coating such as spectral and angular transmittance, reflectivity, phase and retardation can be evaluated for the beam incident on the beam splitter.

[0062] Of course, preferably, the total thickness of the beam splitter (especially when measured along the first direction) is the same as the total thickness of the substrate and all coatings (especially when measured along the first direction, respectively).

[0063] Optionally, the maximum phase difference criterion is met for a beam splitter having a temperature between 0°C and 60°C, such as 20°C (e.g., the ambient temperature may be within this range). In other words, the phase difference of the beam splitter is preferably evaluated when its temperature is within the temperature range. Thus, for a beam having a specific angle of incidence (e.g., 30°) and a specific wavelength, the evaluated phase difference may be greater than 30° if the temperature of the beam splitter is outside the range.

[0064] It is clear to those skilled in the art that the beam splitter optionally has a defined reflectivity and / or a defined transmittance for a specific light beam incident thereon. The beneficial effect of the coating (in combination with the substrate) is that partial reflection of the specific light beam can be achieved while the phase of the specific light beam after transmission through the beam splitter can be precisely controlled.

[0065] Optionally, the term "main surface" (of an element) may be understood as the main surface having the largest surface among the main surfaces. An element may have more than one main surface. For example, a substrate (such as a substrate of a beam splitter) may have two main surfaces (which are parallel to each other). For example, a beam splitter may have two main surfaces, one of which is the outer surface of a coating.

[0066] In one embodiment, alternatively or additionally, it may be preferred that the specific wavelength is between 500nm and 600nm, in particular 550nm, 546nm or 587nm. Wavelengths selected from this range are beneficial because they are very suitable for augmented reality applications. For example, the specific wavelength may be between 500nm and 550nm or between 550nm and 600nm.

[0067] In one embodiment, alternatively or additionally, it may be preferred that the absolute value of the phase difference is less than or equal to 20°, less than or equal to 15°, less than or equal to 10°, less than or equal to 7°, less than or equal to 5°, less than or equal to 3°, or less than or equal to 1°.

[0068] In one embodiment, alternatively or additionally, it may be preferred that the absolute value of the phase difference is greater than or equal to 0.5°, greater than or equal to 1°, greater than or equal to 2°, or greater than or equal to 5°.

[0069] Preferably, the absolute value of the phase difference is greater than or equal to 10° and less than or equal to 30°. This is a trade-off between higher manufacturing costs and improved image quality.

[0070] Preferably, the refractive index n of the coating is c The refractive index n of the substrate s Correspondingly, or the refractive index of the coating (n c ) and the refractive index of the substrate (n s ) at a specific wavelength is between 0.95 and 1.05, preferably between 0.99 and 1.01, and more preferably between 0.995 and 1.005, and / or wherein the refractive index of the substrate (n s ) and the refractive index of the coating (n c ) has an absolute value of less than 1.00, less than 0.50, less than 0.10, less than 0.07, less than 0.05, less than 0.03, less than 0.02, less than 0.01, less than 0.005, less than 0.001, or less than 0.0005; and / or is greater than 0.0001, greater than 0.0002, greater than 0.0003, or greater than 0.0004.

[0071] Preferably, the specific wavelength is between 450 and 650 nm, preferably between 500 nm and 600 nm, in particular 525 nm, 546 nm, 550 nm or 587 nm.

[0072] This allows a soft transition between coating and substrate for a particular light beam, which has proven to be particularly beneficial for improving image quality.

[0073] Preferably, the refractive index of the coating is the average refractive index of the coating.

[0074] In one embodiment, alternatively or additionally, it may be preferred that the coating has at least two layers and / or that the coating has between 1 and 5000, between 2 and 50, between 5 and 40, or between 7 and 35 layers.

[0075] If the coating is a multi-layer coating, the image quality at a specific wavelength or a specific wavelength range can be selectively improved.

[0076] According to the present invention, if there is no coating with a suitable refractive index, the refractive index of the coating is precisely adjusted by combining one or more layers with a low refractive index and one or more layers with a high refractive index to achieve the target refractive index of the coating.

[0077] For the purposes of the present invention, in particular for a wavelength of 550 nm and / or for a specific wavelength, a layer with a low refractive index refers to a layer having a refractive index lower than that of the substrate, and a layer with a high refractive index refers to a layer having a refractive index higher than that of the substrate.

[0078] Preferably, the major surfaces of all layers of the coating are parallel to each other and / or to the major surface of the substrate.

[0079] Preferably, especially for a wavelength of 550 nm and / or a specific wavelength, the absolute value of the difference between the minimum refractive index of one of the layers and the maximum refractive index of one of the layers is less than 1.5, preferably less than 1.3, preferably less than 1.0, preferably less than 0.70, preferably less than 0.50, preferably less than 0.30, preferably less than 0.10, preferably less than 0.05, preferably less than 0.01.

[0080] Preferably, in particular for a wavelength of 550 nm and / or specific wavelengths, the refractive index of each layer is between 1.1 and 2.5.

[0081] In one embodiment, alternatively or additionally, it may be preferred that each layer in the coating has a thickness along the first direction of:

[0082] 1 nm or more, 4 nm or more, 8 nm or more, 10 nm or more, or 15 nm or more; and / or

[0083] Less than or equal to 5000 nm, less than or equal to 3000 nm, less than or equal to 2000 nm, less than or equal to 1000 nm, or less than or equal to 500 nm; and / or

[0084] Between 1 nm and 5000 nm, between 4 nm and 3000 nm, between 8 nm and 2000 nm, between 10 nm and 1000 nm, or between 15 nm and 500 nm.

[0085] The corresponding thickness can be produced using well-known techniques, thereby reducing production costs.

[0086] Preferably, the thickness of each layer whose refractive index is close to the refractive index of the substrate (for example, the refractive index of the layer is 90% to 110% of the refractive index of the substrate) is 10nm to 750nm, the thickness of each layer whose refractive index is high (for example, higher than 110% of the refractive index of the substrate) is 4nm to 50nm, and / or the thickness of each layer whose refractive index is low (for example, less than 90% of the refractive index of the substrate) is 50nm to 200nm.

[0087] In one embodiment, at least one layer of the coating is a dielectric layer, in particular all layers of the coating are dielectric layers, and / or at least one layer of the coating, in particular at least one layer having a thickness of less than 10 nm along the first direction, is composed of and / or includes a metal, such as Ag, and / or the coating has no layer composed of and / or no layer including a metal.

[0088] For dielectric layers, the optical properties of the respective layer can advantageously be controlled. This in turn allows the production of well-defined coatings according to specific requirements for optical properties such as reflectivity and transmittance.

[0089] Metal-free coatings are particularly advantageous for use as beam splitters.

[0090] In one embodiment, alternatively or additionally, it may be preferred that the coating has at least one spatially variable refractive index layer, or consists of one single spatially variable refractive index layer.

[0091] Spatially variable refractive index layers are easily produced using conventional techniques, but have been shown to provide beneficial results in controlling the color shift and optionally the phase of a particular light beam. Spatially variable refractive index layers may be implemented in the form of a rugate design.

[0092] In the sense of the present application, a spatially variable refractive index layer may be a layer whose refractive index varies along a first direction, in particular increases and / or decreases, in particular varies in a cross section.

[0093] Alternatively, or in addition to a spatially variable refractive index layer, a gradient filter may be used.

[0094] In one embodiment, it may alternatively or additionally be preferred that the coating is at least partially applied to the substrate by physical vapour deposition (PVD), preferably sputtering.

[0095] The sputtering process can be precisely controlled such that it is advantageously used to apply a coating (or at least one layer or multiple layers of a multi-layer coating) to a substrate.

[0096] Alternatively, the coating can also be applied to the substrate using CVD (Chemical Vapor Deposition), PICVD (Plasma Pulsed CVD) or ALD (Atomic Layer Deposition).

[0097] In one embodiment, alternatively or additionally, it may be preferred that at least one layer in the coating constitutes a matching layer, and wherein optionally:

[0098] (i) the refractive index and / or light dispersion of the matching layer substantially corresponds to the refractive index and / or dispersion pattern of the substrate, respectively;

[0099] (ii) the ratio of the refractive index of the matching layer to the refractive index of the substrate is between 0.9 and 1.1;

[0100] (iii) the thickness of the matching layer is between 200 nm and 400 nm;

[0101] (iv) the matching layer is arranged directly on the substrate, in particular by deposition and / or as an adhesive layer on said substrate;

[0102] (v) two or more layers in the coating constitute matching layers; and / or

[0103] (vi) The total thickness of all matching layers of the coating is greater than the thickness of any other layer of the coating.

[0104] In another embodiment, alternatively or additionally, it may be preferred that at least one layer in the coating constitutes a matching layer, and wherein optionally:

[0105] (i) the refractive index and / or light dispersion of the matching layer substantially corresponds to the refractive index and / or dispersion pattern of the substrate, respectively;

[0106] (ii) a ratio of the refractive index of the matching layer to the refractive index of the substrate is between 0.95 and 1.05;

[0107] (iii) the thickness of the matching layer is between 15 nm and 750 nm, preferably between 20 nm and 600 nm;

[0108] (iv) the matching layer is arranged directly on the substrate, in particular by deposition and / or as an adhesive layer on the substrate;

[0109] (v) two or more layers in the coating constitute matching layers, and / or

[0110] (vi) the total thickness of all matching layers of the coating is greater than the thickness of any other layer of the coating;

[0111] (vii) The total thickness of all matching layers of the coating is in the range of 250 nm to 1750 nm, preferably in the range of 500 nm to 1500 nm.

[0112] The matching layer matches the phase properties of the coating to those of the substrate. The position of the matching layer in the coating stack can be variable, and the thickness and refractive index of the matching layer can also be a design choice.

[0113] The matching layer does not have to be arranged directly on the substrate. Its position in the coating (eg along the first direction) can be determined by reflectivity and chromaticity conditions.

[0114] It is particularly preferred that the refractive index of the matching layer is identical or similar to the refractive index of the substrate material. It has been shown that in this way a beam splitter can be obtained while also being able to control the phase.

[0115] In particular, matching layers can be used to control the phase of a particular light beam, while other layers of the coating can be used to control the reflectivity and / or transmittance of the beam splitter and / or the coating.

[0116] The total thickness of all matching layers can be measured along the first direction. Similarly, the thickness of other layers of the coating can also be measured along the first direction.

[0117] In a preferred embodiment, the coating has at least two layers, one of which is a matching layer. In another preferred embodiment, the coating has at least three layers, two of which are matching layers.

[0118] The matching layer can be realized in the form of a spatially variable refractive index layer.

[0119] In one embodiment, the coating is identical to a single matching layer.

[0120] If the ratio of the refractive index of the matching layer to the refractive index of the substrate is between 0.95 and 1.05, the values ​​of the refractive index of the matching layer and the substrate are preferably the same.

[0121] Preferably, the absolute value of the difference between the refractive index of the matching layer and the refractive index of the substrate is 0.1 or less, preferably 0.05 or less, preferably 0.02 or less, and preferably 0.01 or less.

[0122] For example, in one embodiment, the thickness of the matching layer is 50 nm to 200 nm, such as 50 nm to 100 nm or 100 nm to 200 nm.

[0123] Preferably, the two refractive indices indicated in this disclosure (the refractive index of the substrate material and the matching layer) are consistent with the wavelength of 550 nm (i.e., the refractive index n d ) and / or specific wavelengths.

[0124] In one embodiment, the matching layer:

[0125] (i) comprising SiO2 and / or Al2O3, in particular in combination with a flint glass containing alkaline earth oxides as substrate material, and / or

[0126] (ii) Made of SiO2, especially in combination with boron-containing crown glass as substrate material.

[0127] In an embodiment, the material of the matching layer may be a mixed material of a high refractive index material (eg, Ta2O5) and a low refractive index material (eg, SiO2), such as a mixture of Al2O3 and SiO2.

[0128] In one embodiment, it is preferred that the coating comprises:

[0129] (i) at least one matching layer, wherein preferably, the ratio of the refractive index of the matching layer to the refractive index of the substrate is between 0.95 and 1.05;

[0130] (ii) at least one layer having a high refractive index, wherein preferably, the ratio of the refractive index of the high refractive index layer to the refractive index of the substrate is greater than 1.05;

[0131] (iii) at least one further layer having a further refractive index, wherein preferably the ratio of the further refractive index of the further layer to the refractive index of the substrate is less than 0.95 and / or greater than 1.05, wherein the at least one further layer is preferably different from the at least one layer having a high refractive index.

[0132] In one embodiment, it is preferred that the coating comprises:

[0133] (i) at least one matching layer, wherein preferably, the ratio of the refractive index of the matching layer to the refractive index of the substrate is between 0.95 and 1.05, and the matching layer is preferably Al2O3;

[0134] (ii) at least one layer having a high refractive index, wherein preferably, the ratio of the refractive index of the high refractive index layer to the refractive index of the substrate is greater than 1.05, and the layer is preferably Ta2O5;

[0135] (iii) at least one layer having a low refractive index, wherein preferably, the ratio of the refractive index of the low refractive index layer to the refractive index of the substrate is less than 0.95, and the layer is preferably SiO2.

[0136] In one embodiment, it is preferred that the coating comprises:

[0137] (i) at least one matching layer, wherein preferably, the ratio of the refractive index of the matching layer to the refractive index of the substrate is between 0.95 and 1.05, and the matching layer is preferably SiO2;

[0138] (ii) having at least a first layer with a high refractive index, wherein preferably, the ratio of the refractive index of the first high refractive index layer to the refractive index of the substrate is greater than 1.05;

[0139] (iii) at least a second layer having a high refractive index, wherein preferably, the ratio of the refractive index of the second high refractive index layer to the refractive index of the substrate is greater than 1.05;

[0140] The first layer and the second layer may include or consist of the same material, or include or consist of different materials, preferably include or consist of different materials, preferably Al2O3 and Ta2O5.

[0141] In an embodiment, the substrate material is or comprises a glass, such as a silicate glass, for example a barium-containing silicate glass. For example, the substrate material may comprise or consist of a flint glass or a crown glass. Optionally, the glass is selected from a flint glass containing alkaline earth oxides, a barium flint glass, a barium crown glass, a boron-containing crown glass, a lanthanum flint glass, a lanthanum crown glass, a dense crown glass, and combinations thereof. It has been shown that corresponding materials, in particular combinations of various materials, can produce a particularly suitable transition between the coating and the substrate for a particular light beam.

[0142] Optionally, the coating may include or consist of one or more components selected from one or more oxides, one or more fluorides, one or more nitrides, one or more sulfides, one or more selenides, one or more metals, and combinations of two or more thereof. For example, the coating may include or consist of one or more components selected from one or more metal oxides, one or more metal fluorides, one or more metal nitrides, one or more metal sulfides, one or more metal selenides, and combinations of two or more thereof. The oxide may be selected from silicon oxide, aluminum oxide, hafnium oxide, tantalum oxide, niobium oxide, titanium oxide, zirconium oxide, yttrium oxide, praseodymium oxide, scandium oxide, tin oxide, chromium oxide, indium oxide, and combinations of two or more thereof. Optionally, the combination of two or more oxides is a mixed oxide. Fluorides may be selected from aluminum fluoride, magnesium fluoride, neodymium fluoride, lanthanum fluoride, yttrium fluoride, gadolinium fluoride, ytterbium fluoride, and combinations of two or more thereof. Nitrides may be selected from aluminum nitride, silicon nitride, and combinations thereof. Sulfides may include zinc sulfide. The selenide may include zinc selenide. The metal may be selected from aluminum, silver, gold, chromium, nickel, and combinations thereof. Optionally, the combination of two or more metals is an alloy. Preferably, the thickness of any metal layer along the first direction is less than 10 nm to provide sufficient transparency. The optional mixed oxide is selected from the oxides of aluminum and praseodymium, aluminum and lanthanum, aluminum and tantalum, praseodymium and titanium, zirconium and titanium, lanthanum and titanium, and niobium and titanium.

[0143] Optionally, the coating may include at least one layer comprising or consisting of one or more oxides, one or more fluorides, one or more nitrides, one or more sulfides, one or more selenides, one or more metals, and combinations of two or more thereof. For example, the layer may include or consist of one or more metal oxides, one or more metal fluorides, one or more metal nitrides, one or more metal sulfides, one or more metal selenides, and combinations of two or more thereof. The oxide may be selected from silicon oxide, aluminum oxide, hafnium oxide, tantalum oxide, niobium oxide, titanium oxide, zirconium oxide, yttrium oxide, praseodymium oxide, scandium oxide, tin oxide, chromium oxide, indium oxide, and combinations of two or more thereof. Optionally, the combination of two or more oxides is a mixed oxide. Fluorides may be selected from aluminum fluoride, magnesium fluoride, neodymium fluoride, lanthanum fluoride, yttrium fluoride, gadolinium fluoride, ytterbium fluoride, and combinations of two or more thereof. Nitrides may be selected from aluminum nitride, silicon nitride, and combinations thereof. The sulfide may include zinc sulfide. The selenide may include zinc selenide. The metal may be selected from aluminum, silver, gold, chromium, nickel, and combinations thereof. Optionally, the combination of two or more metals is an alloy. Preferably, the thickness of any metal layer along the first direction is less than 10 nm to provide sufficient transparency. The optional mixed oxide may be selected from the oxides of aluminum and praseodymium, aluminum and lanthanum, aluminum and tantalum, praseodymium and titanium, zirconium and titanium, lanthanum and titanium, and niobium and titanium.

[0144] Optionally, one or more matching layers may include or consist of one or more components selected from one or more oxides, one or more fluorides, one or more nitrides, one or more sulfides, one or more selenides, one or more metals, and combinations of two or more thereof. For example, the layer may include or consist of one or more components selected from one or more metal oxides, one or more metal fluorides, one or more metal nitrides, one or more metal sulfides, one or more metal selenides, and combinations of two or more thereof. The oxide may be selected from silicon oxide, aluminum oxide, hafnium oxide, tantalum oxide, niobium oxide, titanium oxide, zirconium oxide, yttrium oxide, praseodymium oxide, scandium oxide, tin oxide, chromium oxide, indium oxide, and combinations of two or more thereof. Optionally, the combination of two or more oxides is a mixed oxide. The fluoride may be selected from aluminum fluoride, magnesium fluoride, neodymium fluoride, lanthanum fluoride, yttrium fluoride, gadolinium fluoride, ytterbium fluoride, and combinations of two or more thereof. The nitride may be selected from aluminum nitride, silicon nitride, and combinations thereof. The sulfide may include zinc sulfide. The selenide may include zinc selenide. The metal may be selected from aluminum, silver, gold, chromium, nickel, and combinations thereof. Optionally, the combination of two or more metals is an alloy. Preferably, the thickness of any metal layer along the first direction is less than 10 nm to provide sufficient transparency. The optional mixed oxide is selected from the oxides of aluminum and praseodymium, aluminum and lanthanum, aluminum and tantalum, praseodymium and titanium, zirconium and titanium, lanthanum and titanium, and niobium and titanium.

[0145] Optionally, the coating may include a layer having a first oxide and another layer having a second oxide, the first oxide and the second oxide being the same or different. In certain embodiments, the coating has at least 3 layers, at least 4 layers, at least 6 layers or at least 8 layers. By selecting suitable materials for the individual layers, the optical properties can be matched as desired. For example, the coating may include Ta2O5 and / or SiO2 (especially in combination with boron-containing crown glass as substrate material). Furthermore, optionally, the coating may also include layers of Ta2O5, SiO2 and / or Al2O3, respectively, and / or matching layers including SiO2 and Al2O3 (especially in combination with flint glass containing alkaline earth oxides as substrate material). Furthermore, optionally, the coating may also include layers of hafnium oxide (HfO2) and SiO2, wherein, in one embodiment, the thickness of the hafnium oxide (HfO2) layer is less than the thickness of the SiO2 layer. In addition, optionally, the coating may also include layers of Ta2O5 and SiO2, wherein, in one embodiment, the thickness of the Ta2O5 layer is less than the thickness of the SiO2 layer (which may be from 78nm to 230nm). The material of the coating may be selected according to the desired refractive index or dispersion characteristics.

[0146] In one embodiment, alternatively or additionally, it may be preferred that the thickness of the coating along the first direction is:

[0147] Greater than or equal to 500 nm, greater than or equal to 800 nm, greater than or equal to 1000 nm, greater than or equal to 1500 nm, or greater than or equal to 2000 nm; and / or

[0148] Less than or equal to 3000 nm, less than or equal to 2000 nm, less than or equal to 1500 nm, less than or equal to 1000 nm, or less than or equal to 700 nm; and / or

[0149] Between 500 nm and 3000 nm, between 500 nm and 2000 nm, between 700 nm and 1500 nm, between 1000 nm and 1400 nm, or between 1100 nm and 1300 nm, in particular about 1200 nm.

[0150] Corresponding thicknesses can be produced using well-known techniques, which keeps production costs low.

[0151] In one embodiment, alternatively or additionally, it may be preferred that the refractive index of the coating is:

[0152] 1.45 or more, 1.47 or more, 1.50 or more, 1.51 or more, or 1.60 or more; and / or

[0153] 3.00 or less, 2.50 or less, 2.00 or less, or 1.80 or less.

[0154] It has been shown that the selection of the respective refractive index of the coating is particularly beneficial for improving the image quality. In particular, it has been shown that adjusting the refractive index of the coating as a whole, rather than adjusting the refractive index of each layer of the coating individually, is sufficient to obtain high-quality images.

[0155] Preferably, the refractive index of the coating is the average refractive index of the coating. For example, the value of the above refractive index of the coating may correspond to the value obtained by determining the integral of the refractive index along the thickness of the coating. In the case of discrete layer coatings with uniform refractive index for each single layer, the integral may become a sum.

[0156] For example, for a total coating thickness (particularly thickness measured along a first direction) of d and a coating / its individual layers having a local refractive index of n(x), the average refractive index of the coating can be determined using the following formula:

[0157]

[0158] For example, if the refractive index n of the substrate is s , satisfying the condition The refractive index of the coating can then be considered to match that of the substrate.

[0159] The refractive index of the coating is preferably a weighted average of the local refractive indices over the thickness of the coating.

[0160] In one embodiment, the thickness of the substrate along the first direction is:

[0161] 0.1 mm or more, 0.5 mm or more, 0.7 mm or more, 1.0 mm or more, or 5.0 mm or more; and / or

[0162] Less than or equal to 20.0 mm, less than or equal to 15.0 mm, less than or equal to 10.0 mm, less than or equal to 7.0 mm, or less than or equal to 5.0 mm; and / or

[0163] Between 0.1 mm and 20.0 mm, between 0.5 mm and 10.0 mm, between 1.0 mm and 5.0 mm, between 2.0 mm and 4.0 mm, or between 2.0 mm and 3.0 mm.

[0164] Corresponding thicknesses can be produced using well-known techniques, which keeps production costs low.

[0165] In one embodiment, the refractive index of the substrate is:

[0166] 1.45 or more, 1.47 or more, 1.50 or more, 1.51 or more, or 1.60 or more; and / or 3.00 or less, 2.50 or less, 2.00 or less, or 1.80 or less.

[0167] It has proven to be particularly advantageous to select a corresponding refractive index of the substrate for improving the image quality.

[0168] The term "refractive index" (refractive index of a substrate) used herein may be defined as an indicator of the light bending ability of a substrate.

[0169] For example, the value of the above refractive index of the substrate may correspond to a value obtained by determining the integral of the refractive index along the thickness of the substrate material. In the case of a discrete layer substrate where the refractive index of each single layer is uniform, the integral may become a sum.

[0170] For example, for a total thickness of the substrate (particularly the thickness measured along the first direction) of d and a local refractive index of the substrate of n(x), the average refractive index of the substrate can be determined using the following formula: :

[0171]

[0172] The refractive index of the substrate is preferably a weighted average of the local refractive indices over the thickness of the substrate.

[0173] Preferably, the refractive index is specified for a wavelength of 550 nm and / or a specific wavelength.

[0174] Preferably, the refractive index of the substrate is an average refractive index of the substrate.

[0175] In one embodiment, alternatively or additionally, it may be preferred that the Abbe number v of the substrate d for:

[0176] 15 or more, 30 or more, 40 or more, 50 or more, 70 or more, or 80 or more; and / or

[0177] 95 or less, 80 or less, 70 or less, 50 or less, 40 or less, 30 or less, or 20 or less; and / or

[0178] Between 15 and 95, between 35 and 80, or between 40 and 70, such as 44 or 64.

[0179] It has been shown that the selection of a corresponding Abbe number of the substrate is particularly advantageous for improving the image quality.

[0180] Preferably, the Abbe number ν of the substrate d is the average Abbe number of the substrate.

[0181] In one embodiment, alternatively or additionally, it may be preferred that the absorption coefficient of the substrate is less than 0.4, less than 0.3, less than 0.2, less than 0.1, less than 0.05, less than 0.01, less than 0.005, or less than 0.001.

[0182] Depending on the corresponding absorption coefficients, multiple beam splitters can also be used in series without a significant loss of intensity, so that high image quality is maintained under these conditions as well.

[0183] The term "absorption coefficient" as used herein can be defined as a measure of the exponential decay of the beam intensity, i.e., the value of the downward e-folding distance of the original intensity when the energy of the beam intensity passes through a unit thickness (e.g., one meter) of the substrate material, so that the attenuation coefficient is 1m -1 This means that after the radiation passes through 1 meter, the radiation will be reduced by e times to 1 / e, and for a coefficient of 2m -1 of materials, it will reduce e 2 times or reduced to 1 / e 2 .

[0184] Preferably, the absorption coefficient of the substrate is specified for a wavelength of 550 nm and / or a specific wavelength.

[0185] In one embodiment, it may be preferred, alternatively or additionally, that the base plate is substantially cubic, in particular substantially plate-shaped.

[0186] A substrate of corresponding shape can be easily manufactured. For example, a wafer with a coating can be used, from which a number of beam splitters can then be cut, with a portion of the wafer representing the substrate.

[0187] In one embodiment, alternatively or additionally, it may be preferred that the substrate comprises glass, such as acid-resistant and / or alkali-resistant glass, in particular Group 1 and Group 2 glass according to ISO 719:1985, and / or is non-tempered glass.

[0188] Glass is particularly preferred because the optical properties can be precisely controlled.

[0189] It may be beneficial to use untempered (ie unhardened) glass, since otherwise polarization may occur at the interface of the substrates.

[0190] In one embodiment, alternatively or additionally, it may be preferred that the absolute value of the difference between the refractive index of the substrate and the refractive index of the coating is:

[0191] 1.00 or less, 0.50 or less, 0.10 or less, 0.07 or less, 0.05 or less, 0.03 or less, 0.02 or less, 0.01 or less, 0.005 or less, 0.001 or less, or 0.0005 or less; and / or

[0192] 0.0001 or more, 0.0002 or more, 0.0003 or more, or 0.0004 or more.

[0193] It is advantageous to adjust the values ​​of the refractive indices of the substrate and the coating separately to provide a beam splitter for high quality images.

[0194] Preferably, the refractive index of the substrate and / or the coating is the average refractive index of the substrate and / or the coating.

[0195] Preferably, the two refractive indices are specified for a wavelength of 550 nm and / or a specific wavelength.

[0196] In one embodiment, alternatively or additionally, it may be preferred that a coating is arranged on both main surfaces of the substrate, wherein optionally the two coatings are identical, in particular structurally identical, in particular starting in each case from the substrate.

[0197] The second coating layer may act as a stress compensating layer to compensate for the stress caused by the first coating layer.

[0198] If both major surfaces of the substrate are coated, a phase difference can be observed after a particular beam has been transmitted through the first coating, the substrate and the second coating. In addition, the value of the total thickness of the beam splitter is calculated as the thickness of the two coatings and the thickness of the substrate.

[0199] Preferably, the two coatings are different.

[0200] Surprisingly, it has been shown that if both sides of the substrate are coated in the proposed manner, in particular if the structure of both coatings is identical, it is even possible to generate two reflected beams with one beam splitter while still being able to control the phase in a precise manner. By coating both main surfaces of the substrate, the beam splitter is preferably essentially a double beam splitter in one piece.

[0201] It is understood by those skilled in the art that in each case, starting from the substrate, the structure of the two coatings is identical, in particular when starting from the substrate in a first direction and in the opposite direction, the two coatings have the same structure, in particular the same layer sequence (in particular identical in terms of material and / or thickness).

[0202] In one embodiment, alternatively or additionally, it may be preferred that the beam splitter partially reflects and / or partially transmits a specific light beam incident thereon.

[0203] Preferably, the reflectivity and transmittance of the beam splitter are controlled by the optical properties of the coating, the optical properties of the substrate, and / or a combination of both.

[0204] In one embodiment, alternatively or additionally, it may be preferred that, in particular for light of a certain wavelength incident on the beam splitter, in particular for light of a certain wavelength incident on the beam splitter at an angle of 30° to the optical axis of the beam splitter, and / or for a refractive index value n e , the coating has:

[0205] A reflectivity of at least 0.03 and / or at most 0.35;

[0206] A transmittance of at least 0.65 and / or at most 0.97; and / or

[0207] An absorbance of at least 0.001 and / or at most 0.01.

[0208] It has been shown that corresponding values ​​of the reflectivity, transmittance and / or absorbance of the coating of the beam splitter are particularly preferred for providing a high-quality image.

[0209] Preferably, the reflectivity, transmittance and / or absorbance of the coating is specified for a wavelength of 550 nm and / or a specific wavelength, respectively.

[0210] In one embodiment, the reflectivity of the coating is between 0.03 and 0.09, or between 0.05 and 0.15, or between 0.1 and 0.25, or between 0.2 and 0.29. For example, the reflectivity is between 0.03 and 0.29 or between 0.03 and 0.24.

[0211] In one embodiment, for the reflectivity R, absorbance A and transmittance T of the coating, respectively, the equation R+T+A=1 holds, wherein optionally, the absorbance A is between 0.001 and 0.01, the reflectivity R is between 0.03 and 0.35, and the transmittance T is between 0.65 and 0.97.

[0212] By measuring the reflectance R and the transmittance T and taking into account the energy saving, the absorbance can be obtained, so that the relationship A=1-RT holds.

[0213] Preferably, the complex refractive index n=nr+i*k (wavelength-dependent) can be used. The value of the extinction coefficient k, like the value of n, can be obtained, for example, from a database of optical constants of the coating material. The relationship with the absorption coefficient α[1 / m] is given by the following expression (at vacuum wavelength λ0):

[0214]

[0215] A, R and T can preferably be determined with the aid of a program for designing the layers of the coating.

[0216] The present invention solves this problem in a second aspect by proposing a stack comprising two or more beam splitters according to the first aspect of the present invention, wherein optionally the beam splitters are arranged one above the other along a stacking direction, in particular the stacking direction is parallel to the first direction and / or parallel to the optical axis of the beam splitter.

[0217] Such a stack is particularly preferred for waveguides used in the field of augmented reality.

[0218] All advantages and options described with respect to the beam splitter according to the first aspect of the invention apply equally to the stack according to the second aspect of the invention. Reference is therefore made here to the previous explanations.

[0219] Preferably, the substrates of the beam splitter are arranged relative to each other such that main surfaces of adjacent substrates face each other and / or are parallel to each other.

[0220] In one embodiment, alternatively or additionally, it may be preferred that beam splitters adjacent to each other along the stacking direction or along a direction anti-parallel to the stacking direction have different, in particular increased or decreased reflectivities and / or different, in particular decreased or increased transmittances for specific portions of the light beam incident thereon.

[0221] Surprisingly, it has been found that even if the light beams contributing to forming the image pass through different numbers of beam splitters, an image having a uniform intensity over all parts of the image can be generated by a corresponding configuration.

[0222] In one embodiment, it may alternatively or additionally be preferred that a specific light beam is directed and / or can be directed along a beam splitter within the stack.

[0223] It is clear to those skilled in the art that, along the propagation path of the specific light beam through the stack, the specific light beam is incident on the first beam splitter of the at least two beam splitters. Then, the portion of the specific light beam transmitted on the corresponding previous beam splitter is incident on each subsequent beam splitter of the at least two beam splitters.

[0224] For example, consider a stack with three beam splitters A, B, and C (with beam splitter A at the top, beam splitter C at the bottom, and beam splitter B between beam splitters A and B), and a particular beam is incident on beam splitter A. The transmitted portion of the particular beam is then incident on beam splitter B. The transmitted portion of the beam incident on beam splitter B is incident on beam splitter C.

[0225] In one embodiment, alternatively or additionally, it may be preferred that at least two or all beam splitters are bonded together by means of adhesive, optical contact and / or low temperature bonding (LTB).

[0226] The present invention solves this problem in a third aspect by proposing a method of manufacturing a beam splitter, the method comprising providing a substrate and arranging at least one coating on at least one main surface of the substrate, thereby obtaining a beam splitter according to the first aspect of the invention.

[0227] Surprisingly, it has been shown that the production of a beam splitter can be carried out easily in the manner described.

[0228] In one embodiment, the second main surface of the substrate is also coated, in particular the same coating as applied to the first main surface of the substrate.The second coating is preferably used for stress compensation.

[0229] Example

[0230] According to Examples 1 to 5 of the present invention, the color shift and phase shift of several beam splitters were evaluated. The beam splitters used for evaluation consisted of a substrate made of glass (e.g., boron-containing crown glass (e.g., N-BK7) or dense crown glass (e.g., N-SK2)) with a thickness of 1 mm and a multilayer coating applied on one main surface of the substrate. The materials used and their refractive indices at a wavelength of 550 nm are summarized in Table 1.

[0231] Table 1: Exemplary substrate and coating materials used

[0232] Material n@550nm illustrate N-BK7 1.519 substrate N-SK2 1.610 substrate <![CDATA[Ta2O5]]> 2.186 Layer Material H <![CDATA[Al2O3]]> 1.670 Layer Material M <![CDATA[SiO2]]> 1.479 Layer Material L

[0233] Detailed information on specific substrate and coating materials and their thicknesses are summarized in Table 2 below. In addition, the refractive indices of the substrate and coating are shown, as well as the phase shift for a specific angle.

[0234] Table 2: Characteristics of Examples 1 to 5

[0235]

[0236]

[0237] The color shift characteristics of Examples 1 to 5 at several incident angles are summarized in Tables 1 to 7. The color shift is calculated as follows: (1) Using the color coordinates x inc =0.333,y inc = 0.333 of the incident beam (also called the “partial beam”), (2) evaluating the CIE x, y coordinates x for the transmitted beam (also called the “transmitted (partial) beam”) t and t , and the CIE x,y coordinates x for the reflected beam (also called the "reflected (partial) beam") r and r , (3) Calculate the color shift of the transmitted and reflected beams as follows:

[0238] Chromatic shift Δx of the transmitted beam t =│x inc -x t │andΔy t =│y inc -y t │;

[0239] Color shift Δx of the reflected beam r =│x inc –x r │andΔy r =│y inc –y r │.

[0240] Table 3: CIE x, y color coordinates and color shift - Example 1

[0241] Angle of incidence <![CDATA[x r ]]> <![CDATA[y r ]]> <![CDATA[Δx r ]]> <![CDATA[Δy r ]]> <![CDATA[x t ]]> <![CDATA[y t ]]> <![CDATA[Δx t ]]> <![CDATA[Δy t ]]> 15° 0.327 0.316 0.006 0.017 0.333 0.334 0.000 0.001 23° 0.332 0.337 0.001 0.004 0.333 0.334 0.000 0.001 30° 0.325 0.331 0.008 0.002 0.334 0.334 0.001 0.001 38° 0.335 0.331 0.002 0.002 0.333 0.334 0.001 0.001 45° 0.320 0.338 0.013 0.005 0.334 0.334 0.001 0.001

[0242] Table 4: CIE x, y color coordinates and color shift - Example 2

[0243]

[0244]

[0245] Table 5: CIE x, y color coordinates and color shift - Example 3

[0246] Angle of incidence <![CDATA[x r ]]> <![CDATA[y r ]]> <![CDATA[Δx r ]]> <![CDATA[Δy r ]]> <![CDATA[x t ]]> <![CDATA[y t ]]> <![CDATA[Δx t ]]> <![CDATA[Δy t ]]> 55° 0.326 0.343 0.007 0.010 0.336 0.331 0.003 0.002 58° 0.326 0.330 0.007 0.003 0.336 0.336 0.003 0.003 60° 0.329 0.339 0.004 0.006 0.335 0.332 0.002 0.001 63° 0.329 0.346 0.004 0.013 0.335 0.328 0.002 0.005 65° 0.326 0.332 0.007 0.001 0.338 0.335 0.005 0.002

[0247] Table 6: CIE x, y color coordinates and color shift - Example 4

[0248] Angle of incidence <![CDATA[x r ]]> <![CDATA[y r ]]> <![CDATA[Δx r ]]> <![CDATA[Δy r ]]> <![CDATA[x t ]]> <![CDATA[y t ]]> <![CDATA[Δx t ]]> <![CDATA[Δy t ]]> 48° 0.324 0.335 0.009 0.002 0.334 0.334 0.001 0.001 52° 0.331 0.336 0.002 0.003 0.333 0.334 0.000 0.001 56° 0.332 0.335 0.001 0.002 0.333 0.334 0.000 0.001 60° 0.330 0.335 0.003 0.002 0.334 0.334 0.001 0.001 64 0.329 0.334 0.004 0.004 0.334 0.334 0.001 0.001 68° 0.337 0.330 0.004 0.003 0.333 0.334 0.000 0.001

[0249] Table 7: CIE x, y color coordinates and color shift - Example 5

[0250] Angle of incidence <![CDATA[x r ]]> <![CDATA[y r ]]> <![CDATA[Δx r ]]> <![CDATA[Δy r ]]> <![CDATA[x t ]]> <![CDATA[y t ]]> <![CDATA[Δx t ]]> <![CDATA[Δy t ]]> 15° 0.337 0.339 0.004 0.006 0.333 0.333 0.000 0.000 20° 0.335 0.328 0.002 0.005 0.333 0.335 0.000 0.002 25° 0.333 0.328 0.000 0.005 0.333 0.335 0.000 0.002 30° 0.331 0.331 0.002 0.002 0.334 0.334 0.001 0.001 35° 0.336 0.329 0.003 0.004 0.333 0.335 0.000 0.002 40° 0.327 0.333 0.006 0.000 0.335 0.334 0.002 0.001

[0251] It can be seen that all beam splitters according to Examples 1 to 5 produce very low color shifts in a wide range of incident angles after transmitting or reflecting the incident light beam. In addition, as can be seen in Table 2, all beam splitters exhibit low phase shifts at specific incident angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0252] Various aspects of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments in light of the accompanying drawings, in which:

[0253] Figure 1a A schematic diagram showing an embodiment of a beam splitter according to the present invention includes other illustrations;

[0254] Figure 1b A schematic diagram of the reference substrate is shown. Other conditions are similar to Figure 1a Same as shown in;

[0255] Figure 2 is a schematic diagram of a stack according to the second aspect of the present invention; and

[0256] Figure 3 is a flow chart of a method according to the third aspect of the present invention.

[0257] Figure 4a and 4b is a CIE 1931xy chromaticity diagram showing the chromaticity of a light beam when it is transmitted through the beam splitter according to Example 1 ( Figure 4a ) or reflected by a beam splitter according to Example 1 ( Figure 4b ) after the color shift. DETAILED DESCRIPTION

[0258] Figure 1a A beam splitter 1 is shown, which comprises a substrate 3 made of glass and a coating 5 applied on a first main surface 7 of the substrate 3. The coating 5 has three layers 9a, 9b and 9c, which are made of different materials.

[0259] By combining three layers 9a, 9b and 9c with different refractive indices, the refractive index of the coating 5 is adjusted in a precise manner so as to achieve a target refractive index of the coating. For example, layer 9a can have a low refractive index of 1.5, layer 9b can have a high refractive index of 2.2, and layer 9c can have a refractive index of 1.7, so that the refractive index of the coating 5 can be 1.61. Layer 9a or layer 9c can be a matching layer that matches the refractive index of the substrate material of 1.61. By combining different layers, the reflectivity and transmittance of the beam splitter and the resulting color shift can be defined with the help of other layers, while the phase of the incident light beam can also be controlled (especially by the matching layer).

[0260] The thickness of the substrate 3 along the first direction D1 is T S , the first direction D1 is parallel to the normal vector N of the first main surface 7 (and also parallel to Figure 1a The thickness of the coating 5 along the first direction D1 is T. C The total thickness of the beam splitter 1 along the first direction D1 is T T , which is T C and T S sum. exist Figure 1a , a specific light beam 11 incident on the beam splitter 1 is shown. The specific light beam has chromaticity x, y according to the CIE standard. The direction of the specific light beam is indicated by an arrow. The angle of incidence (also called "incident angle") is, for example, 30°, which is the angle α between a vector parallel to the first direction D1 (such as the normal vector N of the first main surface 7) and a vector parallel to the specific light beam 11. The specific wavelength of the specific light beam 11 is 550nm. In practice, the specific light beam propagates within the prism 13, which is closely attached to the beam splitter 1. The prism 13 is used as a coupling element, so that the specific light beam 11 can be coupled into the beam splitter 1.

[0261] A portion of the specific light beam 11 is reflected by the beam splitter 1, thereby generating a reflected partial light beam 15 (also referred to as a "reflected light beam"). The reflected light beam has chromaticity x, y according to the CIE standard. Another portion of the specific light beam 11 is transmitted through the beam splitter 1, thereby generating a transmitted partial light beam 17 (also referred to as a "transmitted light beam"), wherein the transmitted light beam has chromaticity x, y according to the CIE standard.

[0262] A schematic representation of the propagation path of a specific light beam 11 within the beam splitter 1 (ie within the coating 5 and the substrate 3) is shown by a dotted line.

[0263] The transmitted part of the specific light beam 11 (ie the partial light beam 17 ) leaves the beam splitter 1 at an exit point 19 , which is located on a second main surface 21 of the substrate 3 , and the second main surface 21 points in a direction opposite to the first main surface 7 .

[0264] Figure 1b Shown with Figure 1a The same arrangement as shown in FIG. 1 is shown in FIG. 2 , wherein the same features are marked with the same reference numerals. However, the beam splitter 1 has been replaced by a reference substrate 23 which is identical to the substrate 3 but has a thickness T along the first direction D1. T In other words, the thickness of the reference substrate 23 is Figure 1a The overall thickness of the beam splitter 1 is the same.

[0265] If Figure 1a The phase of the transmitted partial beam 17 in Figure 1b If the phase of the transmitted partial beam 17 in is compared (in both cases at the corresponding exit point 19), a phase difference with an absolute value of less than 30° can be evaluated.

[0266] This makes the beam splitter 1 preferably used in augmented reality applications, since the phase difference can be limited and the reflectivity / transmittance can also be defined as described above.

[0267] Figure 2 A stack 50 according to the second aspect of the invention is shown. The stack 50 comprises three beam splitters 51, 53 and 55 according to the first aspect of the invention. The beam splitters 51, 53 and 55 may be at least partially or fully as described above with reference to Figure 1a and 1b The beam splitter 1 is implemented as described above.

[0268] The beam splitters 51 , 53 and 55 are arranged one above the other along a stacking direction S, wherein the stacking direction is parallel to the first direction D1 .

[0269] Figure 3 A flow chart 100 is shown of a method according to the third aspect of the invention.

[0270] In 101, a substrate (e.g., substrate 1) is provided. In 103, a coating (e.g., coating 5) is arranged on one of the main surfaces (e.g., first main surface 7) of the substrate. In 105, a beam splitter (e.g., beam splitter 1) according to the first aspect of the invention is obtained.

[0271] The features disclosed in the description, the drawings and the claims can be essential for the realization of different embodiments of the invention either individually or in any combination.

[0272] Figure 4a and Figure 4b The CIE 1931 xy color diagram is shown, illustrating the incident light beam (also called the "specific light beam") after being transmitted through the beam splitter ( Figure 4a ) and reflection ( Figure 4b) (also called "partially transmitted beam" or "transmitted beam" and "reflected partial beam" or "reflected beam"). Figure 4a Shown are the positions of incident light beams (circles) whose chromaticity according to CIE x,y is 0.333; 0.333, and the resulting chromaticity of the transmitted light beams (diamonds) depending on the angle of incidence of the particular light beam. Figure 4b Shown are the positions of incident beams (circles) whose chromaticity according to CIE x,y is 0.333; 0.333, and the resulting chromaticity of reflected beams (triangles) depending on the angle of incidence of the particular beam.

[0273] Reference numerals list

[0274] 1 Beam splitter

[0275] 3 substrate

[0276] 5 Coating

[0277] 7 First main surface

[0278] Levels 9a, 9b, 9c

[0279] 11 Specific beam

[0280] 13 Prism

[0281] 15 Reflected partial beam

[0282] 17 Transmitted partial beam

[0283] 19 exit point

[0284] 21 Second main surface

[0285] 23 Reference substrate

[0286] 50 stacks

[0287] 51 Beam Splitter

[0288] 53 Beam Splitter

[0289] 55 Beam Splitter

[0290] 100 Flowchart

[0291] 101 Provide substrate

[0292] 103 Arranging the coating on the substrate

[0293] 105 Get beam splitter

[0294] α (incident) angle

[0295] D1 First direction

[0296] N Normal vector

[0297] S Stacking direction

[0298] T C thickness

[0299] T S thickness

[0300] T T thickness.

Claims

1. A beam splitter comprising a substrate made of a substrate material and at least one coating arranged on at least one main surface of the substrate, wherein: The substrate and all coatings have a total thickness along a first direction parallel to a normal vector to the major surface, and where, for a particular light beam with a particular chromaticity defined by CIE x and y, The specific light beam is incident on the beam splitter along the second direction at at least one incident angle sandwiched between a vector pointing in the first direction and a vector pointing in the second direction, the incident angle being in the range of 15° to 75°, preferably 15° to 45°, more preferably 20° to 42°, and particularly preferably an angle of 32°, and the specific light beam is partially transmitted through the beam splitter and partially reflected by the beam splitter, the difference between the CIE x-coordinate of the particular light beam after transmission through the beam splitter and the CIE x-coordinate of the light beam after transmission through the beam splitter is less than 0.05, preferably less than 0.025, and more preferably less than 0.005, and / or The difference between the CIE y coordinate of the specific beam after the beam is transmitted through the beam splitter and the CIE y coordinate of the beam after transmission through the beam splitter is less than 0.05, preferably less than 0.025, and more preferably less than 0.

005.

2. The beam splitter according to claim 1, wherein: The refractive index n of the coating c The refractive index n of the substrate s Correspondingly, or at a specific wavelength, the refractive index of the coating (n c ) and the refractive index of the substrate (n s ) is between 0.95 and 1.05, preferably between 0.99 and 1.01, and more preferably between 0.995 and 1.005, and / or Wherein, the refractive index of the substrate (n s ) and the refractive index of the coating (n c ) has an absolute value of less than 1.00, less than 0.50, less than 0.10, less than 0.07, less than 0.05, less than 0.03, less than 0.02, less than 0.01, less than 0.005, less than 0.001, or less than 0.0005; and / or is greater than 0.0001, greater than 0.0002, greater than 0.0003, or greater than 0.0004.

3. The beam splitter according to claim 1 or 2, wherein: The beam splitter has a wavelength-dependent transmittance and a wavelength-dependent reflectance, wherein, for at least one specific angle of incidence, preferably for all angles of incidence in the range of 15° to 60°, preferably in the range of 15° to 45° and / or in the range of 20° to 42°, and / or at angles of incidence of 30° and / or 60°, In the wavelength range of 420nm to 680nm, the beam splitter has a maximum transmittance T (420-680)最大 and minimum transmittance T (420-680)最小 , where T (420-680)最大 and T (420-680)最小 The difference is less than 10%, preferably less than 7%, more preferably less than 5%, particularly preferably less than 3%, and / or In the wavelength range of 420nm to 680nm, the beam splitter has a maximum reflectivity R (420-680)最大 and minimum reflectivity R (420-680)最小 , where R (420-680)最大 and R (420-680)最小 The difference is less than 10%, preferably less than 7%, more preferably less than 5%, particularly preferably less than 3%, and / or At a wavelength of 430 nm, the beam splitter has a maximum transmittance T (430)最大 and minimum transmittance T (430)最小 , where T (430)最大 and T (430)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or At a wavelength of 430 nm, the beam splitter has a maximum reflectivity R (430)最大 and minimum reflectivity R (430)最小 , where R (430)最大 and R (430)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or At a wavelength of 535 nm, the beam splitter has a maximum transmittance T (535)最大 and minimum transmittance T (535)最小 , where T (535)最大 and T (535)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or At a wavelength of 535 nm, the beam splitter has a maximum reflectivity R (535)最大 and minimum reflectivity R (535)最小 , where R (535)最大 and R (535)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or At a wavelength of 565 nm, the beam splitter has a maximum transmittance T (565)最大 and minimum transmittance T (565)最小 , where T (565)最大 and T (565)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%, and / or At a wavelength of 565 nm, the beam splitter has a maximum reflectivity R (565)最大 and minimum reflectivity R (565)最小 , where R (565)最大 and R (565)最小 The difference is less than 10%, preferably less than 5%, more preferably less than 3%, particularly preferably less than 2%.

4. A beam splitter according to any one of the preceding claims, wherein: The difference between the CIE x coordinate of the specific light beam and the CIE x coordinate of the reflected light beam is less than 0.05, preferably less than 0.025, and more preferably less than 0.005, and / or The difference between the CIE y coordinate of the specific light beam and the CIE y coordinate of the reflected light beam is less than 0.05, preferably less than 0.025, and more preferably less than 0.

005.

5. A beam splitter according to any one of the preceding claims, wherein: The chromaticity x of the specific light beam according to the CIE standard is in the range of 0.283 to 0.383, preferably in the range of 0.300 and 0.360, more preferably in the range of 0.310 and 0.350, and particularly preferably in the range of 0.320 to 0.340, and / or the chromaticity y of the specific light beam according to the CIE standard is in the range of 0.283 to 0.383, preferably in the range of 0.300 to 0.360, more preferably in the range of 0.310 to 0.350, and particularly preferably in the range of 0.320 to 0.

340.

6. A beam splitter according to any one of the preceding claims, in, For light with a specific wavelength in the range of 450nm to 650nm, the light is incident on the beam splitter along a second direction at an incident angle of 30° sandwiched between a vector pointing in the first direction and a vector pointing in the second direction, and after the specific light beam is transmitted through the beam splitter, the absolute value of the phase difference of the specific light beam is less than or equal to 30° compared with a case where the beam splitter is replaced with a reference substrate made of a substrate material and having a thickness equal to the total thickness of the beam splitter under the same other conditions, Preferably, the absolute value of the phase difference is less than or equal to 20°, less than or equal to 15°, less than or equal to 10°, less than or equal to 7°, less than or equal to 5°, less than or equal to 3°, or less than or equal to 1°; and / or greater than or equal to 0.5°, greater than or equal to 1°, greater than or equal to 2°, or greater than or equal to 5°.

7. A beam splitter according to any one of the preceding claims, wherein: The coating has at least two layers and / or the coating has between 1 and 5000, between 2 and 50, between 5 and 40, or between 7 and 35 layers.

8. A beam splitter according to any one of the preceding claims, wherein: The thickness of each layer in the coating along the first direction: 1 nm or more, 4 nm or more, 8 nm or more, 10 nm or more, or 15 nm or more; and / or Less than or equal to 5000 nm, less than or equal to 3000 nm, less than or equal to 2000 nm, less than or equal to 1000 nm, or less than or equal to 500 nm; and / or Between 1 nm and 5000 nm, between 4 nm and 3000 nm, between 8 nm and 2000 nm, between 10 nm and 1000 nm, or between 15 nm and 500 nm.

9. A beam splitter according to any one of the preceding claims, wherein: At least one layer of the coating is a dielectric layer, in particular all layers of the coating are dielectric layers, and / or at least one layer of the coating, in particular at least one layer having a thickness of less than 10 nm along the first direction, is composed of and / or includes a metal, such as Ag, and / or the coating does not have a layer composed of a metal and / or does not have a layer including a metal.

10. A beam splitter according to any one of the preceding claims, wherein: The coating has at least one spatially variable refractive index layer or consists of a single spatially variable refractive index layer.

11. A beam splitter according to any one of the preceding claims, wherein: The coating is at least partially applied to the substrate by physical vapor deposition (PVD), preferably sputtering.

12. A beam splitter according to any one of the preceding claims, wherein: At least one layer of the coating constitutes a matching layer, and wherein optionally: (i) the refractive index and / or light dispersion of the matching layer substantially correspond to the refractive index and / or dispersion pattern of the substrate, respectively; (ii) a ratio of the refractive index of the matching layer to the refractive index of the substrate is between 0.95 and 1.05; (iii) the thickness of the matching layer is between 15 nm and 750 nm, preferably between 20 nm and 600 nm; (iv) the matching layer is arranged directly on the substrate, in particular by deposition and / or as an adhesive layer on the substrate; (v) two or more layers in the coating constitute matching layers; and / or (vi) the total thickness of all matching layers of the coating is greater than the thickness of the other layers of the coating; (vii) The total thickness of all matching layers of the coating is in the range of 250 nm to 1750 nm, preferably in the range of 500 nm to 1500 nm.

13. A beam splitter according to any one of the preceding claims, wherein: The matching layer comprises or consists of the following components: a. one or more components selected from one or more oxides, one or more fluorides, one or more nitrides, one or more sulfides, one or more selenides, one or more metals, and combinations of two or more thereof; and / or b. one or more components selected from one or more metal oxides, one or more metal fluorides, one or more metal nitrides, one or more metal sulfides, one or more metal selenides, and combinations of two or more thereof, Preferably, wherein a. The oxide is selected from silicon oxide, aluminum oxide, hafnium oxide, tantalum oxide, niobium oxide, titanium oxide, zirconium oxide, yttrium oxide, praseodymium oxide, scandium oxide, tin oxide, chromium oxide, indium oxide, and a combination of two or more thereof; b. The fluoride is selected from aluminum fluoride, magnesium fluoride, neodymium fluoride, lanthanum fluoride, yttrium fluoride, gadolinium fluoride, ytterbium fluoride, and a combination of two or more thereof; c. The nitride is selected from aluminum nitride, silicon nitride, and a combination thereof; d. the sulfide is zinc sulfide; e. the selenide is zinc selenide; and / or f. The metal is selected from aluminum, silver, gold, chromium, nickel, and combinations thereof.

14. A beam splitter according to any one of the preceding claims, wherein: The thickness of the coating along the first direction is greater than or equal to 500 nm, greater than or equal to 800 nm, greater than or equal to 1000 nm, greater than or equal to 1500 nm, or greater than or equal to 2000 nm; and / or Less than or equal to 3000 nm, less than or equal to 2000 nm, less than or equal to 1500 nm, less than or equal to 1000 nm, or less than or equal to 700 nm; and / or Between 500 nm and 3000 nm, between 500 nm and 2000 nm, between 700 nm and 1500 nm, between 1000 nm and 1400 nm, or between 1100 nm and 1300 nm, in particular about 1200 nm.

15. A beam splitter according to any one of the preceding claims, wherein: The refractive index of the coating is: 1.45 or more, 1.47 or more, 1.50 or more, 1.51 or more, or 1.60 or more; and / or 3.00 or less, 2.50 or less, 2.00 or less, or 1.80 or less.

16. A beam splitter according to any one of the preceding claims, wherein: The thickness of the substrate along the first direction is: 0.1 mm or more, 0.5 mm or more, 0.7 mm or more, 1.0 mm or more, or 5.0 mm or more; and / or Less than or equal to 20.0 mm, less than or equal to 15.0 mm, less than or equal to 10.0 mm, less than or equal to 7.0 mm, or less than or equal to 5.0 mm; and / or Between 0.1 mm and 20.0 mm, between 0.5 mm and 10.0 mm, between 1.0 mm and 5.0 mm, between 2.0 mm and 4.0 mm, or between 2.0 mm and 3.0 mm.

17. A beam splitter according to any one of the preceding claims, wherein: The refractive index of the substrate is: 1.45 or more, 1.47 or more, 1.50 or more, 1.51 or more, or 1.60 or more; and / or 3.00 or less, 2.50 or less, 2.00 or less, or 1.80 or less.

18. A beam splitter according to any one of the preceding claims, wherein: The base plate is substantially cuboidal, in particular substantially plate-shaped.

19. A beam splitter according to any one of the preceding claims, wherein: The substrate comprises glass, such as acid-resistant and / or alkali-resistant glass, in particular group 1 and group 2 glass according to ISO 719:1985, and / or non-tempered glass.

20. A beam splitter according to any one of the preceding claims, wherein: A coating is arranged on both main surfaces of the substrate, wherein optionally the two coatings are identical, in particular structurally identical, in particular starting in each case from the substrate.

21. A beam splitter according to any one of the preceding claims, wherein: In particular, for light of a specific wavelength incident on the beam splitter, in particular for light of a specific wavelength incident on the beam splitter at an angle of 32° to the optical axis of the beam splitter, and / or for a refractive index value n e , the coating has: A reflectivity of at least 0.03 and / or at most 0.35; A transmittance of at least 0.65 and / or at most 0.97; and / or An absorbance of at least 0.001 and / or at most 0.

01.

22. A stack comprising two or more beam splitters according to any one of the preceding claims, wherein optionally the beam splitters are arranged one above the other along a stacking direction, in particular the stacking direction is parallel to the first direction and / or parallel to the optical axis of the beam splitter.

23. A stack according to claim 22, wherein: Beam splitters that are adjacent to each other along the stacking direction or along a direction antiparallel to the stacking direction have different, in particular increased or decreased, reflectivities and / or different, in particular decreased or increased transmittances for certain light beams incident thereon.

24. A stack according to any one of the preceding claims 22 to 23, wherein The specific light beam is directed and / or can be directed along the beam splitter within the stack.

25. A method of manufacturing a beam splitter, the method comprising providing a substrate and arranging at least one coating on at least one main surface of the substrate, thereby obtaining a beam splitter according to any of the preceding claims 1 to 21.

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