Method and device for testing optical composite elements

Abstract

Method for testing the optical properties of an optical composite component (1), wherein the composite component (1) comprises a plurality of interconnected transparent elements (8) and reflective layers (9), wherein the transparent elements (8) and the reflective layers (9) are arranged such that light coupled at an input section (4) is split in a first segment (3) of the composite component (1) with several transparent elements (8) into a plurality of first partial beams (41), which are guided along different paths in the composite element (1), and wherein the first partial beams (41) are partially reflected multiple times in a second segment (5), also with several transparent elements (8), such that several second partial beams (42) emerge from a side surface (11) by means of the partial reflection, wherein the second partial beams (42) are detected by means of a detector (12).and- a quality index is determined from the signals of the detector (12) for several second partial beams (42), and wherein- the several second partial beams (42), from whose signals the quality index is determined, are preferably selected according to an aggregation rule such that the quality index can be assigned to a specific part of the composite component (1).

Description

The invention relates generally to the production of optical composite elements comprising a plurality of joined optical elements in which light is guided and deflected by reflection. In particular, the invention relates to the testing of such optical composite components with regard to their optical quality. State of the art For so-called "augmented reality" applications, special glasses are used that can project additional information into the user's field of vision via an optical system. This information is typically coupled into the lens via a projector, guided along the lens by light, and then decoupled, thus making it visible to the viewer. Various optical elements, coupled together within the lens, are used for coupling, light guidance, and decoupling. Such lenses are known, for example, from EP 1 562 066 B1, US 2023 / 0314689 A1, and WO 2021 / 001841 A1. These lenses, designed as image light guides, can be manufactured by bonding together a multitude of optical components. These components have reflective, and in particular partially reflective, layers that split the image information, coupled in via a projector, for example, into several partial beams, guide them through the light guide, and then couple them out again, allowing the viewer to perceive the image information in addition to the surrounding image. Both the geometric accuracy of the individual components, and especially the design of the reflective layers and the relative alignment of the components, can influence the optical properties of the light guide with regard to image quality.For example, the modulation transfer function (MTF) can be negatively affected by tolerances in the alignment and surface quality of individual parts and layers, leading to a reduction in image sharpness. It would be desirable not only to determine quality factors such as the MTF, but also, in the case of a poor quality factor, to identify which parts of the optical composite component are responsible. This is the object of the present invention. The determination of certain quality factors of optical components is described in the prior art. For example, DE 103 21 680 A1 discloses an optical method for determining the quality of pellicles, i.e., transparent protective materials used, for example, in lithography. DE 10 2022 132 453 A1 describes a method for determining the quality of images obtained with a test object, for example, with optics for augmented reality or virtual reality systems. The determination of the geometric and optical quality of optical components, such as ophthalmic lenses, is disclosed in DE 601 32 551 T2. Disclosure of the invention To solve the problem, a method for testing the optical properties of an optical composite component is provided, wherein the composite component comprises a plurality of interconnected transparent elements and reflective layers, wherein the transparent elements and the reflective layers are arranged such that light coupled at an input section is split into a plurality of first partial beams in a first segment of the composite component with several transparent elements, which are guided along different paths in the composite element, and wherein the partial beams are partially reflected multiple times in a second segment, also with several transparent elements, such that several second partial beams emerge from a side surface due to the partial reflection, and wherein the second partial beams are detected by means of a detector.and- a quality index is determined, in particular calculated, from the signals of the detector for several second partial beams, and wherein- the several second partial beams from whose signals the quality index is calculated are preferably selected according to an aggregation rule such that the quality index can be assigned to a specific part of the composite component. A corresponding device for carrying out this method comprises a holder for a composite component and a light source arranged opposite the holder such that light from the light source coupled into a coupling section of the composite element is split in a first segment of the composite component with several transparent elements into a plurality of first partial beams, which are guided along different paths in the composite element, and wherein the partial beams are partially reflected multiple times in a second segment, also with several transparent elements (8), such that several second partial beams emerge from a side surface by the partial reflection, wherein the device comprises a detector for detecting the second partial beams, and an evaluation device, wherein the evaluation device is configured- to calculate a quality factor from the detector signals for several second partial beams and, for this purpose, to select the several second partial beams from whose signals the quality factor is determined, in particular according to an aggregation rule, such that the quality factor can be assigned to a specific part of the composite component. Such a part can be a region or section of the composite component. Particularly preferably, the selection of the second partial beams is carried out in such a way that the quality index can be assigned to a very specific element of the composite component. In particular, such an element can be a specific reflective layer. In a further development of the method and the device, it is therefore provided that the second partial beams for determining the quality index are selected such that the light of these selected partial beams has been reflected by a specific reflective layer. This reflection can also involve a first partial beam from which the second partial beam originates. A partial beam, as defined in this disclosure, need not be a sharp, linear beam of light, such as that produced by a laser. For the purposes of this disclosure, partial beams can also be bundles of rays. This is the case, for example, when these partial beams transmit image information. For an optical composite component within the meaning of this disclosure, glass elements are particularly suitable as transparent elements. However, plastic elements, such as those made of PMMA or polycarbonate, as well as plastics commonly used for spectacle lenses, would also be conceivable. The invention will be described in more detail below with reference to the figures and without limitation thereto. Identical reference numerals denote identical or similar elements. Figure 1 shows an optical composite component in a device for testing the optical properties of the composite component. Figure 2 shows an optical composite component together with a diagram comparing several quality parameters. Figure 3 shows a cross-section through an optical composite component. Figure 4 shows a beam path for a single first partial beam in a composite component according to Figure 3. Figure 5 shows a simulation of the position of the exit points of second partial beams on the second segment. Figure 6 shows a corresponding simulation with partially removed reflective layers in the first segment. Figure 7 shows a corresponding simulation with partially removed reflective layers in the second segment. Figure 8 shows a corresponding simulation on a composite element without a mixer segment.Fig. 9: A corresponding simulation on a composite element with a mixer segment, with marked beam exit points that are added compared to Fig. 7 due to the presence of the mixer segment. Fig. 10: A crosshair as image information for determining a modulation transfer function and an arrangement of measurement points. Fig. 11: A side view of a composite component and a camera as a detector, as well as the beam path of second partial beams. Fig. 12: Values ​​of the modulation transfer function in two mutually perpendicular directions for different colors. Fig. 13 shows values ​​of the modulation transfer function in two mutually perpendicular directions at different measurement points. Figs. 14, 15 to 16: Contour diagrams of the modulation transfer function. Fig. 1 shows an optical composite component 1, which is particularly suitable as a spectacle lens or screen for augmented reality applications. The composite component 1 is used to examine its optical quality in a device 2 for testing its optical properties, or rather, its optical quality. The composite component 1 is composed of many interconnected transparent elements 8. Generally, without limiting it to the example shown, glass elements are preferred as transparent elements 8. The function of the composite component is also based on the fact that the image information to be displayed to the user is split into many different partial beams and spatially distributed towards the user's eye. Specifically, reflective layers 9 are provided for this purpose. In a preferred embodiment, the surfaces of the transparent elements 8 are coated with reflective layers 9. The transparent elements 8 are connected to each other at these coated surfaces, in particular by bonding. In this way, reflective layers 9 are obtained that extend within the composite component 1. For the sake of clarity, the adhesive layers are not shown in Fig. 1. The light, particularly for use with the composite component 1 in the form of an image signal, is coupled in via a coupling section 40 of the composite component 1. In a particularly preferred embodiment, a projector 70 for projecting images can be provided as the light source 7 for coupling in an image signal, without being limited to the example given. According to one embodiment, a coupling mirror 43, preferably tilted relative to the side surface 11 of the composite component 1, is provided in the coupling section 40. This mirror can also be designed as a reflective layer 9. In this way, the light, in particular the image information, can be emitted in a direction perpendicular to the side surface 11 and is then deflected inside the composite component 1 in a direction along the side surface 11. This emitted primary beam 40 is split into a plurality of first partial beams 41 in a first segment 3 of the composite component 1. During the splitting at the partially reflective reflective layers 9, which are arranged obliquely to the primary beam 40, the light is also deflected so that the first partial beams 41 are guided along different paths in the composite element 1. In particular, these first partial beams 41 can also run parallel and spaced apart from each other, as in the example shown in Fig. 1.In a second segment 5, the reflective layers 9 are inclined to the side surface 11 of the composite element 1, so that the light is partially reflected and exits the side surface 11. Accordingly, the first partial rays 41 are partially reflected multiple times by the reflective layers 9 in the second segment 5, such that the partial reflection from one side surface 11 results in several second partial rays 42 exiting spatially distributed across the side surface 11. For clarity, the second partial rays 42 are shown only for one of the first partial rays 41. To understand the figure, it should be noted that, viewed from above on the side surface 11, the second partial rays 42 essentially run in the direction of view and therefore do not run in the plane of the figure as depicted. The same applies to the primary ray 40 between the light source 7 and the coupling mirror 43.For better representation, a quasi-perspective view was chosen for these rays, so that the rays are visible in the drawing plane. The method and device 2 according to this disclosure can now be used to investigate the optical quality of these second partial beams 42. In particular, it can also be determined which area, or even which specific element in the composite component 1, is responsible for any deterioration in image quality. The evaluation is carried out with a detector 12, which is arranged to detect the second partial beams 42. Specifically, a camera 120 is provided as the detector 12.An evaluation unit 15 is connected to the detector 12, or camera 120. This unit is configured to calculate a quality index from the signals of the detector 12 for several second partial beams 42. To this end, the evaluation unit selects the several second partial beams 42, from whose signals the quality index is determined, in particular according to an aggregation rule, such that the quality index can be assigned to a specific part of the composite component 1. The several partial beams 42 can be acquired individually and sequentially, for example, by repositioning the detector 12 each time to acquire another second partial beam 42 using a suitable device. Alternatively or additionally, several second partial beams 42 can be acquired simultaneously by the detector 12. In general, but especially for an embodiment in which a projector 70 is provided as the light source and a camera 120 as the detector 12, it is advantageous for accurate measurement if the exit pupil of the light source 7, i.e., preferably of the projector 70, is smaller than the entrance pupil of the detector 12, i.e., in particular of a camera 120. In this way, the exit points of the second partial beams 42, and thus also their optical path, can be clearly defined and reliably detected. Preferably, the entrance pupil is at least twice as large. Calculating the quality factor can generally involve summing, and in particular averaging, the signals from detector 12. For example, a quality factor can be determined for every second partial beam 42 of the selected set. Then, an average quality factor can be calculated from the individual values. If the signals of certain second partial beams 42 are evaluated and other second partial beams 42 are disregarded, this can also be understood as an evaluation with a simple weighting of the second partial beams 42 with weights 0 and 1. However, it is generally also possible to perform an additional weighting within the set of second partial beams 42 selected for determining the quality index according to an aggregation rule. The aggregation rule can therefore include, in addition to the selection, a weighting in which one or more weights are different from one. Without being limited to specific embodiments, a further development of the method and the correspondingly configured device provides that the signals of the second partial beams 42 are weighted for determining the quality index.Such further training is useful, for example, if certain second partial beams 42 are more strongly influenced by the optical properties of a part of the composite element 1 than others. Tracing the path of the second partial beams 42 shown in the example of Fig. 1, it is evident that all partial beams 42 were reflected at the same reflective layer 9 in the first segment 3, since these second partial beams 42 are derived from a single first partial beam 41 reflected at this reflective layer. A quality factor resulting from the calculation of the signals of these second partial beams 42 is therefore influenced by this single reflective layer 9. In general, without being limited to this specific example, a preferred embodiment of the method and the corresponding evaluation device 2 provides that the second partial beams 42 are selected for determining the quality factor such that the light of these selected partial beams 42 was reflected at a specific reflective layer 9.However, the light of the partial beams 42 also passes through a multitude of other optical elements on its path from the coupling point of the primary beam to the coupling point at the side surface 11. The influence of a specific part of the composite component 1 on the quality index can be particularly well extracted when the quality indexes for different quantities of partial beams 42 are considered. Therefore, in a further development of the method and the correspondingly configured device 2, it is generally provided that the quality index is compared with at least one other quality index determined from a different quantity of second partial beams 42. Fig. 2 shows an example. On the right side of Fig. 2, a composite element 1 similar to Fig. 1 is shown. The beam path of all first and second partial beams 41, 42 to a primary beam 40 is depicted here. The second partial rays 42, emitted perpendicular to the image plane, are symbolized by dots. In this example, the primary ray 40 is split into eleven first partial rays 41 in the first segment 3. As in the example of Fig. 1, each of the second partial rays 42 originating from a specific first partial ray 41 has therefore been reflected at a specific facet, or a specific reflective layer 9, in the first segment 3. However, due to the other elements in the beam path, the quality index can also be influenced by these other elements. This can be determined by comparison. On the left, a bar chart is shown with the quality indexes for the quantities of second partial rays 42 corresponding to each first partial ray 41. Each bar thus represents the quality index for each row of the resulting matrix-like arrangement of the second partial rays 42.The aggregation rule used to select the partial beams 42 in this example therefore consists of selecting the second partial beams 42 that were extracted from the same first partial beam 41. In this example, all twelve of these second partial beams 42 can be selected. It would also be conceivable to select a subset, such as using only every third partial beam 42. The comparison now shows that, for example, the reflection at the reflection layer 9 closest to the coupling mirror 43 can be assigned a higher quality index compared to, for example, the third and fourth reflection layers 9 in this direction. The former quality index is above the mean value shown as a dashed line, while the reflections at the third and fourth reflection layers yield below-average quality indexes. With such an evaluation, elements with poorer optical performance can therefore be located.If systematic effects are observed, the optical performance can then be increased by adjusting the manufacturing process for the composite element 1. Figure 2 also shows that the influence of the reflective layers 9 of the second segment 5 on the optical performance of the composite element 1 can be investigated in a similar manner. In this example, all second partial beams 42 in a column of the matrix-like distribution of the second partial beams 42 are reflected by the same reflective layer 9 of the second segment 5. In this case, essentially the second partial beams 42 of the individual columns of the matrix-like distribution of the second partial beams 42 can be selected, which therefore represents a different aggregation rule. However, the aggregation rule can be somewhat more complex here, since a first partial beam 41 may also produce two second partial beams 42 at the same reflective layer 9 in the second segment 5 through two reflections. The exact aggregation rules can be obtained, for example, by simulation.An examination of the quality indicators obtained in this way can then be carried out by comparison, analogous to what has already been described using the bar chart. In general, without being limited to specific examples and types of quality indicators, a quality indicator can also be determined from at least two previously determined quality indicators in a further development of the method and the device. Such a further quality indicator determined from two or more quality indicators can be referred to as a higher-level quality indicator. For example, such a higher-level quality indicator can be a difference, a quotient, a sum, or a product of previously determined quality indicators. As mentioned above, a mean value of the quality indicators for second partial beams 42, each derived from a first partial beam 41, can be used. From the diagram in Fig. 2, the standard deviation of the individual quality indicators Q could also be determined or calculated as a further higher-level quality indicator. Figures 1 and 2 illustrate how, by selecting and evaluating the signals of certain second partial beams, conclusions can be drawn about the quality of individual reflective layers 9 in the first segment 3 and second segment 5. Often, such an optical composite component 1 contains further optical components. For example, a partially reflective layer 9 can be provided, either horizontally or extending parallel along the side surface 11. Such a reflective layer can be used to split the first partial beams, so that the split beams are then guided along different paths in the second segment 5. This allows brightness variations to be homogenized. Figure 3 shows a cross-section of an optical composite component 1. The composite component 1 is typically disk-shaped with parallel side surfaces 11 and 13.Contrary to what is shown, the composite component 1 can also have a slight curvature. Between the first segment 3 and the second segment 5, with its reflective layers 9 oriented obliquely to the side surfaces 11, 13, a mixer segment 14 with a reflective layer 9 lying parallel to the side surfaces 11, 13 is arranged. The beam path for a single first partial beam 41 in such a composite component 1 is shown schematically in Fig. 4. As can be seen, a first partial beam 41 is split into two partial beams 410, 411 at the reflective layer 9 of the mixer segment 14, from which second partial beams 42 are then separated at the reflective layers 9 of the second segment 5 and emerge from the side surface 11. If the reflective layer 9 in the mixer segment were omitted, the partial beam 410 would be missing. Accordingly, all second partial beams 42 originating from this partial beam 410 would also be absent. These second partial beams 42 originating from the partial beam 410 thus contain information about the optical quality of the mixer segment 14 and its reflective layer 9.In this case, the aggregation rule for selecting the second partial beams is more complex compared to the selection rules for the reflection layers 9 of the first and second segments 3, 5. In the example in Fig. 4, the second partial beams 42 to be selected are shown with solid lines, and the partial beams 42 to be disregarded are shown with dashed lines. It should be noted that the spatial position of the second partial beams 42, and thus also the respective aggregation rule, depends on the path of the first partial beam 41, and this in turn depends on the path of the primary beam. Therefore, the illustration is purely illustrative.In general, without limiting itself to the example shown, a further development of the method and the correspondingly configured device 2 provides that the optical composite element 1 has a mixer segment 14 arranged in the beam direction in front of the second segment 3, preferably between the first segment 3 and the second segment 5, which has a partially reflective reflective surface 9 lying parallel to the side surface 11 inside the composite element 1, wherein, for determining the quality factor, such second partial beams 42 are selected which originate from a partial beam 410 reflected at this reflective surface 9. To selectively detect the second partial beams 42, a movement device 18 is generally provided in one embodiment of the device. This device allows the detector 12 and the optical composite component 1 to be moved relative to each other in order to position the detector 12 at specific measurement positions relative to the optical composite component 1, in particular to scan the side surface 11 at the predetermined measurement positions. In the example, the detector 12 is attached to the movement device 18 to move it while the composite component 1 is held stationary. The reverse configuration with the composite element 1 moving, or a combined movement, is also possible. For the evaluation of image signals, it is generally preferred, without limiting it to the example, that the detector 12 includes a camera 120. The following figures graphically illustrate aggregation rules generated by simulations for the reflections discussed above at individual reflection surfaces 9 in the first and second segments 3, 5 and the mixer segment 14. Fig. 5 shows the brightly colored exit points of the second partial beams 42 on a 12 x 12 mm area of ​​the second segment 5. As can already be seen from the schematic representation in Fig. 2, rows of exit points of the second partial beams 42 result, which are split off from first partial beams 41. The first partial beams 41 are generated, as described, at specific successive reflection layers 9 in the first segment 3. The underlying partial beams 41 are labeled 41-3 to 41-8 in Fig. 5. Fig. 6 shows the same simulation, with some reflection layers removed in the first segment 3. Only the reflection layers with the indices 41-3 and 41-8 remain. Accordingly, two rows of exit points for the second partial beams 42 result. In Fig. 7, a composite element was used as a basis in which all reflective layers 9 are present in the first segment, but only two reflective layers 9 of the second segment are present at the edge of the image field. As already explained, the remaining second partial beams 42, which are to be selected according to the corresponding aggregation rule, are not necessarily arranged precisely in the columns of a matrix-shaped grid. Rather, the beam path results in slight shifts of the exit points in the x-direction and also in multiple second partial beams 42 from a single first partial beam 41. In any case, the pattern shown can be used as an aggregation rule for a primary beam emitted according to the simulation in order to check the optical quality of the respective reflective layers 9 of the second segment 5. Fig. 8 shows a corresponding simulation of a composite element 1 without mixer segment 14, or rather, its reflective surface running parallel to the side surface 11. As can be seen, compared to the simulation in Fig. 5 of a composite element 1 with mixer segment 14, groups of second partial beams 42 are missing along obliquely running stripes. The effect is easily recognizable when considering the schematic beam path in Fig. 4. Fig. 9 shows a corresponding simulation of a composite element with mixer segment 14, i.e., the same simulation as in Fig. 5. However, the second partial beams that are added compared to Fig. 8 are marked here with circles around the beam exit points. These marked second partial beams correspond accordingly to an aggregation rule for checking the optical quality of the mixer segment using a quality index. A relative comparison similar to that in Fig. 2 can be made by determining the quality index with the values ​​shown in Fig.8 visible second partial beams. Here, too, a higher-level quality index, determined from the quality indexes of the sets of partial beams shown in Fig. 8 and Fig. 9, can be particularly informative about the quality of the reflective layer in the mixer segment 14. For example, the modulation transfer functions for the subsets of second partial beams 42 that were transmitted and reflected at the reflective layer 9 can be compared. There are numerous quality indicators that can be determined using the method and the device 2 designed according to the method. Among others, the following quality indicators are particularly advantageous for assessing product quality: - the modulation transfer function in at least one image direction, optionally also color-dependent, - a comparison, in particular a ratio of the modulation transfer functions for two different image directions, - angular deviations of the direction of the second partial beams 42, - the transmission efficiency, in particular also color-dependent, - a shift of color coordinates, - the dispersion in the emerging second partial beams 42, - the polarization of the second partial beams 42. Some such quality parameters, such as transmission efficiency, could also be determined using non-imaging measurement methods. For example, a laser could be used as a light source with a simple detector, such as a photodiode. A non-imaging measurement would also be conceivable for polarization. The polarization of the light is influenced by reflections at the reflective layers 9. Additionally, a λ / 2 plate 16, as shown in Figures 1 and 3, can be provided. This plate rotates the polarization direction of the light so that effective reflection at the reflective layers 9 in the second segment 5 is enabled. This plate is very thin, and tolerances can cause correspondingly large fluctuations in the polarization state. Another effect is possible birefringence in the transparent elements 8. However, as already mentioned in Fig. 1, it is generally preferred to use a projector 70 to couple in a primary beam 40 containing image information and to evaluate this image information with a detector 12 in the form of a camera 120. To determine the modulation transfer function for a second partial beam 42, an image with one or more test structures, for example crosshairs, dots, or circles, can be coupled in, and the image in the respective second partial beam 42 can be captured by the camera 120. These images can then be evaluated with regard to their sharpness in two different image directions, in the case of a crosshair, approximately perpendicular to the branches of the crosshair, in order to determine the modulation transfer function. Such a crosshair 15 with two spatial directions y, x is shown in Fig. 10, partial image (a).Partial image (b) shows an area on the second segment 5 with nine measuring points XP1 - XP9, which are used for the further embodiments. The measuring points lie in a square area of ​​approximately 17 x 17 mm. Each measurement point represents an exit point of a second partial beam 42. In the following examples, the exit points, or rather the spatial arrangement of the second partial beams 42, are not explicitly chosen in such a way that the image signal is isolated from and can be attributed to specific elements, such as a particular reflective layer. Rather, the measurement points, or the captured second partial beams, are chosen to be centered with respect to the user's eye. Nevertheless, these measurement positions can provide information about the quality of specific areas of the composite component 1, so that the quality index can be assigned to a specific part of the composite component 1.Thus, the optical path is shortest for measuring point XP3 and the second partial beam emerging there, and longest for measuring point XP7, since the first segment 3 is located to the right of the section shown and the coupling of the primary beam takes place from the upper right, near measuring point XP3. As explained with reference to Fig. 4, the second partial beams 42 emerging from the measuring points XP1 - XP9 can be detected by moving the detector 12, preferably a camera 120, to the measuring positions by means of a suitable movement device 18, or by scanning the side surface 11. According to an alternative or additional embodiment, a rapid measurement can also be carried out by capturing all measuring points XP1 - XP9, or the second partial beams emerging there, together in a single camera 120. For this purpose, the camera 120 is positioned at a greater distance so that, as shown in Fig. 11, the partial beams 42 are captured and imaged by the lens 121 of the camera. The lens 121 can, in particular, be designed as a telescope. The side view corresponds to a view from the left of the arrangement of measuring points XP1 - XP9 shown in Fig. 10.In the illustration, three measuring points and their second partial beams 42 are superimposed. Such an arrangement, in which several partial beams are detected simultaneously, is of course not limited to this specific example. It would also be conceivable to detect all partial beams 42 shown in Fig. 5 simultaneously, provided the entire area shown can be imaged at once. Therefore, without being limited to specific examples, one embodiment provides that the detector 12 comprises a camera 120, which is arranged at such a distance from the side surface 11 of the composite component 1 that several partial beams 42 are detected simultaneously by the camera 120, these second partial beams 42 emerging from the side surface 11 at a distance of at least 10 mm, preferably at least 15 mm. If several second partial beams 42 are detected together, as in Fig.As shown in Figure 11, a corresponding test pattern containing several test structures, such as crosshairs, can also be coupled into the projector. For the example in Figure 10, sub-image (b), an image with nine crosshairs 15 in a 3 x 3 matrix arrangement can be coupled in, which are then visible at the respective measurement positions XP1 - XP9. Fig. 12 shows modulation transfer function (MTF) values ​​in two mutually perpendicular directions for different colors. Sub-image (a) shows the values ​​1 / 2Ny_ROIV for the y-direction corresponding to sub-image (a) of Fig. 10, and sub-image (b) shows the values ​​1 / 2Ny_ROIH for the x-direction. The partial beam from the central measurement point XP5 was evaluated. The measured values ​​1 / 2Ny_ROIV and 1 / 2Ny_ROIH are a measure of the sharpness of the depicted reticle 15, expressed as multiples of half the Nyquist frequency of the human eye. Specifically, the values ​​represent the percentage contrast for a pattern with 10 lines per degree of viewing angle. The MTF was evaluated for the colors blue, green, red and white, corresponding to the abbreviations B, G, R, W. Fig. 12 shows that the resolution, or the MTF for both spatial directions, is hardly color-dependent, since all values ​​are close to the mean value shown as a dashed line.However, the MTF values ​​differ significantly between the vertical (image (a)) and horizontal (image (b)) directions, with better sharpness achieved in the vertical direction. For the following examples of the spatial distribution of the MTF, only the color green was evaluated. Fig. 13 shows one-way analyses of the values ​​1 / 2Ny_ROIV (part (a), y-direction) and 1 / 2Ny_ROIH (part (b), x-direction). For both directions, a slight decrease in resolution is observed within all rows of measurement points. The resolution is highest at measurement points XP3, XP6, and XP9 located to the right of the beam entry into the second segment 5, and lowest at the most distant measurement points XP1, XP4, and XP7. Although the measurement points cannot be assigned to specific reflective layers, they nevertheless demonstrate the influence of the reflective layers 9 of the second segment 5 as part of the composite element 1. In other words, the measured values, and in particular their decrease with the number of intervening reflective layers 9, can be interpreted as quality factors. Using these measured values ​​1 / 2Ny_ROIV and 1 / 2Ny_ROIH, contour diagrams of the MTF can also be created for a measuring range as shown in Fig. 10, sub-image (b). Fig. 14 shows a contour diagram of the MTF, specifically of the value 1 / 2Ny_ROIH (i.e., the resolution in the x-direction) of a composite element 1 with good optical resolution. For understanding the diagrams, it should be noted that the indexing of the spatial directions in Fig. 14 and the following illustrations is inverted compared to the orientation shown in Fig. 10, sub-image (b). The measuring point XP3 is located in the contour diagram not in the upper right, but in the lower left. The measured values ​​are shown to the left of the contour lines. Here too, the best resolution is found in the area of ​​measurement position XP3, in this case the lower left, as can be seen from the contour with a 1 / 2Ny_ROIH value of 31. Interestingly, a slight minimum is visible in the middle of the area with a 1 / 2Ny_ROIH value of 23. A continuous decrease in resolution, as in the example of Fig. 13, is therefore not necessarily the case. Fig. 15 shows another example of such a contour diagram. Here, the highest resolution values ​​are found in the upper left, which corresponds to the area around measurement point XP9 in Fig. 10, sub-image (b). The optical quality can still be considered good with regard to the MTF. However, the contour profile indicates a slight degradation in the first segment 3, or rather in one or more of the reflection layers 9 in this part. Specifically, the quality factor 1 / 2Ny_ROIH, with its slightly degraded value of 18, can be assigned to the part of the first segment 3 approximately near the coupling section 4. Finally, Fig. 16 shows a contour diagram with poor MTF values. Overall, the resolution drops to comparatively low 1 / 2Ny_ROIH values ​​of 10 over a large area. With appropriately set minimum requirements, such a composite element 1 could be rejected. Although the present invention has been described using preferred embodiments, it is not limited to these, but can be modified in many ways. Reference symbol list 1 Optical composite component 2 Device for testing the optical properties of an optical composite component 1 3 First segment 4 Coupling section 5 Second segment 6 Mount 7 Light source 8 Transparent element 9 Reflective layer 11, 13 Side surface of 1 12 Detector 14 Mixer segment 15 Crosshairs 16 λ / 2 plate 18 Motion device 40 Primary beam 41 First partial beam 42 Second partial beam 43 Coupling mirror 70 Projector 120 Camera 121 Lens 410, 411 Partial beams generated in mixer segment 14

Claims

Method for testing the optical properties of an optical composite component (1), wherein the composite component (1) comprises a plurality of interconnected transparent elements (8) and reflective layers (9), wherein the transparent elements (8) and the reflective layers (9) are arranged such that light coupled at an input section (4) is split in a first segment (3) of the composite component (1) with several transparent elements (8) into a plurality of first partial beams (41), which are guided along different paths in the composite element (1), and wherein the first partial beams (41) are partially reflected multiple times in a second segment (5), also with several transparent elements (8), such that several second partial beams (42) emerge from a side surface (11) by means of the partial reflection, wherein the second partial beams (42) are detected by means of a detector (12).and- a quality index is determined from the signals of the detector (12) for several second partial beams (42), and wherein- the several second partial beams (42), from whose signals the quality index is determined, are preferably selected according to an aggregation rule such that the quality index can be assigned to a specific part of the composite component (1). Method according to the preceding claim, characterized in that the second partial beams (42) are selected for determining the quality index such that the light of these selected partial beams (42) has been reflected at a specific reflective layer (9). Method according to one of the preceding claims, characterized in that the quality indicator is compared with at least one further quality indicator which is determined from another set of second partial beams (42). Method according to one of the preceding claims, characterized in that a superior quality indicator is determined from at least two previously determined quality indicators. Method according to one of the preceding claims, characterized in that the optical composite element (1) has a mixer segment (14) arranged between the first segment (3) and the second segment (5), which has a partially reflective reflective surface (9) lying parallel to the side surface (11) inside the composite element (1), wherein, for determining the quality factor, such second partial beams (42) are selected which are based on a partial beam (410) reflected at this reflective surface (9). Method according to one of the preceding claims, characterized in that at least one of the following quality parameters is determined: - the modulation transfer function in at least one image direction, preferably color-dependent, - a comparison, in particular a ratio of the modulation transfer functions for two different image directions, - angular deviations of the direction of the second partial beams (42), - the transmission efficiency, in particular also color-dependent, - a shift of color coordinates, - the dispersion in the emerging second partial beams (42), - the polarization of the second partial beams (42). Method according to the preceding claim, wherein, to determine the modulation transfer function for a second partial beam (42), an image with one or more test structures is coupled in and the image in the second partial beam (42) is captured by a camera (120) and evaluated with regard to sharpness in two different image directions. Method according to one of the preceding claims, characterized in that the signals of the second partial beams (42) are weighted to determine the quality factor. Device (2) for carrying out the method according to one of the preceding claims, comprising a holder (6) for a composite component (1) and a light source (7) arranged relative to the holder (6) such that light from the light source (7) coupled into a coupling section (4) of the composite element (1) is split in a first segment (3) of the composite component (1) with several transparent elements (8) into a plurality of first partial beams (41), which are guided along different paths in the composite element (1), and wherein the first partial beams (41) are partially reflected multiple times in a second segment (5), also with several transparent elements (8), such that several second partial beams (42) emerge from a side surface (11) by the partial reflection, wherein the device (2) comprises a detector (12) for detecting the second partial beams (42), and an evaluation device (15).wherein the evaluation device (15) is configured to calculate a quality index from the signals of the detector (12) for several second partial beams (42) and to select the several second partial beams (42) from whose signals the quality index is determined, in particular according to an aggregation rule, such that the quality index can be assigned to a specific part of the composite component (1). Device (2) according to the preceding claim, characterized in that the light source (7) comprises a projector (70) for transmitting images. Device (2) according to one of claims 9 and 10, wherein the detector (12) comprises a camera (90). Device (2) according to one of claims 9 to 11, characterized in that the exit pupil of the light source (7), preferably of a projector (70), is smaller than the entrance pupil of the detector (12), preferably of a camera (120). Device (2) according to one of claims 9 to 12, characterized by a movement device (18) with which the detector (12) and the optical composite component (1) can be moved relative to each other in order to position the detector (12) at certain measuring positions relative to the optical composite component (1). Device (2) according to any one of the preceding claims 9 to 13, wherein the detector (12) comprises a camera (120) which is arranged at such a distance from the side surface (11) of the composite component (1) that several partial beams (42) are simultaneously detected by the camera (120), wherein these second partial beams (42) exit at a distance on the side surface (11) of at least 10 mm, preferably at least 15 mm.

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