Systems and methods for generating images of seam-lines in light-guide optical elements

Abstract

A system generates images of seam-lines in an optical structure. The system includes an illumination arrangement with a light source and a collimating lens that outputs a collimated beam towards the optical structure. The illumination arrangement directs the output beam at non-normal angles, causing scattering by seam-lines formed at interfaces within the optical structure. An imaging arrangement is also included, and has an imaging lens and a detector. The imaging lens receives scattered light from the seam-lines while substantially excluding direct light from the light source from reaching the detector. This arrangement ensures that the scattered light from the seam-lines forms a visible image on the detector against a substantially dark background.

Description

[0001] APPLICATION FOR PATENT

[0002] TITLE

[0003] Systems and Methods for Generating Images of Seam-Lines in Light-Guide Optical Elements

[0004] CROSS-REFERENCE TO RELATED APPLICATIONS

[0005] This application claims priority from US Provisional Patent Application No. 63 / 679,779, filed August 6, 2024, whose disclosure is incorporated by reference in its entirety herein. TECHNICAL FIELD

[0006] The present disclosure relates to optical systems, and in particular, it concerns systems and methods for generating images of seam-lines in optical structures such as light-guide optical elements.

[0007] BACKGROUND OF THE INVENTION

[0008] Accurate positioning is needed in both the manufacturing process and inspection process of optical structures, such as a light-guide optical element (LOE) formed from a light-transmitting substrate having parallel major external surfaces and one or more internal partially-reflecting surfaces. For instance, in order to accurately produce a wearable LOE (for example as part of a near eye display) with a desired contour, it is necessary to cut the LOE accurately with respect to the position of the internal elements (e.g., internal surfaces) of the LOE. Furthermore, the optical structure should be accurately positioned in order to allow proper inspection and evaluation of optical performance (via optical inspection tools). In the case of LOEs, the positioning should be such that the internal surfaces are aligned to a requisite orientation and position in accordance with optical system requirements.

[0009] One problem with optical performance evaluation in LOEs is that the seam-lines of the optical structure, for example formed at the interface between the internal surfaces and the major external surfaces, are deliberately designed and manufactured to be as inconspicuous as possible. As a result, the inspection of the requisite orientation and position, typically performed using computerized components implementing image processing / computer vision techniques, is inherently difficult.

[0010] SUMMARY OF THE INVENTION

[0011] Aspects of the present disclosed subject matter, also referred to herein as the disclosure, provide systems and methods for generating images of seam-lines in light-guide optical elements.

[0012] According to the teachings of an embodiment of the present disclosure, there is provided a system for generating an image of seam-lines in an optical structure. The system comprises: an illumination arrangement comprising: a light source for emitting light, and a collimating lens configured to receive light from the light source and to output an output beam, that is collimated to infinity or approximately to infinity, towards the optical structure, the illumination arrangement configured such that the output beam is directed toward the optical structure at non-normal angles so that that the output beam is scattered by the seam-lines, the seam-lines formed at interfaces between internal components of the optical structure and optical surfaces of the optical structure; and an imaging arrangement comprising: an imaging lens configured to receive scattered light from the seam-lines of the optical structure, and a detector configured to sense light received from the imaging lens and to generate an image signal from the sensed light, the imaging lens configured to substantially exclude direct light from the light source from reaching the detector, such that the scattered light from the seam-lines forms a visible image on the detector against a substantially dark background.

[0013] Optionally, the system further comprises an image processing subsystem configured to: receive the image signal from the detector, and perform image analysis on the received image signal in order to determine at least one of position or orientation of the seam-lines in the optical structure.

[0014] Optionally, the light source includes an annular light source.

[0015] Optionally, the light source includes a dipole source.

[0016] Optionally, the light source comprises a reticle having a transparent annular disk. Optionally, the light source is positioned at a focal plane of the collimating lens. Optionally, the imaging lens has a transparent inner portion and an opaque external portion. Optionally, the optical structure is a light-guide optical element having two major external surfaces and at least one internal surface deployed between the two major external surfaces, and the seam-lines are formed at interfaces between the at least one internal surface and the two major external surfaces.

[0017] Optionally, the light emitted by the light source is symmetric around an axis normal to a major external surface of the optical structure.

[0018] Optionally, the light source is configured to emit light for dark-filed illumination.

[0019] There is also provided according to the teachings of an embodiment of the present disclosure a method for generating an image of seam-lines in an optical structure. The method comprises: emitting light from a light source; receiving the emitted light at a collimating lens and outputting an output beam from the collimating lens, the output beam collimated to infinity or approximately to infinity; directing the output beam toward the optical structure at non-normal angles, such that that the seam-lines scatter the output beam, the seam-lines formed at interfaces between internal components of the optical structure and optical surfaces of the optical structure; receiving scattered light from the seam-lines at an imaging lens, receiving the scattered light by the imaging lens includes substantially excluding direct light from the light source from reaching a detector; and sensing the scattered light received from the imaging lens at the detector and generating an image signal from the sensed light, the scattered light from the seam-lines forming a visible image against a substantially dark background.

[0020] Optionally, the method further comprises: receiving, by an image processing subsystem, the image signal from the detector; and performing, by the image processing subsystem, image analysis on the received image signal in order to determine at least one of position or orientation of the seam-lines in the optical structure.

[0021] Optionally, the light source includes an annular light source.

[0022] Optionally, the light source includes a dipole source.

[0023] Optionally, the light source comprises a reticle having a transparent annular disk.

[0024] Optionally, method further comprises: deploying the light source and the collimating lens such that the light source is positioned at a focal plane of the collimating lens.

[0025] Optionally, the imaging lens has a transparent inner portion and an opaque external portion.

[0026] Optionally, the optical structure is a light-guide optical element having two major external surfaces and at least one internal surface deployed between the two major external surfaces, and the seam-lines are formed at interfaces between the at least one internal surface and the two major external surfaces.

[0027] Optionally, the light emitted by the light source is symmetric around an axis normal to a major external surface of the optical structure.

[0028] Optionally, the light emitted by the light source is dark-field illumination.

[0029] Unless otherwise defined herein, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains. Although methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the disclosure, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Some embodiments of the present disclosure are herein described, by way of example only, with reference to the accompanying drawings. With specific reference to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the disclosure. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the disclosure may be practiced. Attention is now directed to the drawings, where like reference numerals or characters indicate corresponding or like components. In the drawings:

[0032] FIG. 1 is a schematic representation of a system, having an illumination arrangement and an imaging arrangement, for generating an image of seam-lines in an optical structure, according to an embodiment of the present disclosure;

[0033] FIG. 2 is a schematic representation of an optical structure implemented as a light-guide optical element (LOE) having two sets of mutually-parallel partially-reflecting internal surfaces that define seam-lines that can be imaged by the optical system of FIG. 1, also showing a collimated beam of illumination from the illumination arrangement impinging the seam-lines at a non-normal angle of incidence;

[0034] FIG. 3 is a side view of the LOE of FIG. 2;

[0035] FIG. 4 is a schematic front view of a light source of the illumination arrangement of FIG. 1, implemented as an annular source, according to an embodiment of the present disclosure;

[0036] FIG. 5 is an image of seam-lines of the LOE of FIG. 2 formed by a detector of the imaging arrangement of FIG. 1 when using the annular source of FIG. 4;

[0037] FIG. 6 is an image similar to the image shown in FIG. 5, also showing a sample tracked seam-line and a reconstructed line, overlaid on the tracked seam-line, that is generated by an image processing subsystem of the system of FIG. 1 ;

[0038] FIG. 7A is an image of seam-lines similar to FIG. 5, but for a case where the illumination from the annular source is not well collimated;

[0039] FIG. 7B is an enlarged view of a region of the image of FIG. 7 A, showing the junction between two seam-lines and a tracked position of the junction;

[0040] FIGS. 8 A and 8B are schematic representations of an optical simulation of the system of FIG. 1, in which the lenses of the illumination arrangement and the imaging arrangement are implemented as paraxial lenses and the object to be imaged is a diffusing cross-shaped pattern;

[0041] FIGS. 9 - 11 are images formed on the detector of the imaging arrangement for different optical simulation scenarios using the optical simulation of FIGS. 8 A and 8B; and

[0042] FIG. 12 is a flow diagram of a method for imaging seam-lines in an optical structure, according to embodiments of the present disclosure.

[0043] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Embodiments of the present disclosure provide systems and methods for generating images of seam-lines in light-guide optical elements.

[0045] The principles of the systems and methods according to present disclosure may be better understood with reference to the drawings accompanying the description. Before explaining at least one embodiment of the disclosure in detail, it is to be understood that the disclosure is not necessarily limited in its application to the details of construction and the arrangement of the components and / or methods set forth in the following description and / or illustrated in the drawings and / or the examples. The embodiments of the disclosure are capable of other embodiments or of being practiced or carried out in various ways.

[0046] Referring now to the drawings, FIG. 1 schematically illustrates a system, generally designated 10, according to a non-limiting embodiment of the present disclosure. The system 10 is configured, among other things, to generate a visible image of features of an object to be imaged. Generally speaking, the system 10 includes an illumination arrangement 12 having a light source 14 and a collimating lens 16, and an imaging arrangement 18 (e.g., a “camera”) having an imaging lens 20 and a detector 22. In the illustrated embodiment, a display an image processing subsystem 24, having at least one processor 26 coupled to a storage medium 28, and a display 29 are also provided.

[0047] An optical structure 30 (the object to be imaged) is deployed in the optical path between the illumination arrangement 12 and the imaging arrangement 18. The optical structure 30 is formed from a light-transparent material, and includes a plurality of features to be imaged, in particular seam-lines that are precisely formed at interfaces (intersections) between internal components of the optical structure 30 and various optical surfaces of the structure 30. The seamlines are not shown in FIG. 1, but are illustrated in FIGS. 2 and 3, and designated 32. The seamlines 32 in the optical structure 30 are inconspicuous.

[0048] The light source 14 is configured to emit light, represented schematically as rays 15. In certain embodiments, the light source 14 is configured to emit light for dark-filed illumination. The collimating lens 16 (which may be implemented as a single lens or as a set of lenses) is configured to receive the emitted light 15 from the light source 14 and to output an output beam (represented schematically as rays 17), that is collimated to infinity or approximately to infinity, towards the optical structure 30. In certain non-limiting embodiments, the collimating lens 16 is implemented as a paraxial lens.

[0049] The illumination arrangement 12 is particularly configured so that the light 15 emitted by the source 14 illuminates the optical structure 30 in such a way so as to enhance the visibility of certain features of the optical structure 30, particularly the seam-lines 32. This is achieved by the configuring the illumination arrangement 12 so that the output beam 17 is directed toward the optical structure 30 at non-normal angles (i.e., such that the beam 17 impinges on the seam-lines 32 of the optical structure 30 at non-normal angles of incidence), such that that the output beam 17 is scattered (or diffracted) by the seam-lines 32 scatter (or diffract) the. In the figure, the light scattered by the seam-lines 32 is represented schematically as rays 31. The scattering effect may also be due, in part, to variations in the optical medium at the seam-lines, specifically the changes in refractive index at the boundary between the external surface of the optical structure and the internal components of the optical structure.

[0050] The non-normal angles can be angles of incidence (measured with respect to the normal to the light-impinging surface of the optical structure 30 that forms the seam-line 32) of at least 80 degrees, but in certain cases may be of at least 85 degrees. In certain cases, the non-normal angles can be grazing angles. Practically speaking, the non-normal angles at which the light 17 impinges the seam-lines 32 may vary considerably with the optical design of the optical structure, including the materials from which the optical structure is constructed.

[0051] Parenthetically, it is noted that as used herein, the term “collimated to infinity” or “approximately to infinity” refers to a condition in which the light rays emitted from the light source and passed through the collimating lens emerge as substantially parallel rays, or rays that exhibit minimal divergence over a relevant working distance. This configuration corresponds to a wavefront that is substantially planar and simulates the behavior of light emanating from or directed toward an object at optical infinity. In practical implementations, perfect collimation is not required. The phrase “approximately to infinity” is intended to encompass configurations in which the output beam exhibits a sufficiently low divergence angle such that, for the purposes of the downstream components (the optical structure and other optical components of the system), the beam behaves as though it were collimated to infinity. It is also noted that although FIG. 1 illustrates the rays of the beam 17 as parallel to the optical axis, this representation is for ease of illustration only. In practice, parallelism of the rays to the optical axis may not be present due to factors such as the type of light source 14, the location of the source 14 (relative to the collimating lens 16), and the illumination pattern generated by the light source 14. Further discussion regarding this will follow in subsequent sections of the present disclosure.

[0052] The imaging lens 20 (which may be implemented as a single lens or as a set of lenses) is configured to receive the scattered light 31 from the seam-lines 32 of the optical structure 30, and to convert the received scattered light 31 into beams of captured light (represented schematically as rays 21) that converge toward the detector 22. In other words, the imaging lens 20 is configured to focus the scattered light 31 from the seam-lines 32 onto the detector 22. In certain non-limiting embodiments, the imaging lens 20 is implemented as a paraxial lens.

[0053] The detector 22 (which may be implemented, for example, as a CCD sensor, CMOS image sensor, photodiode array, avalanche photodiode, etc.) is configured to sense the captured light 21 received from the imaging lens 20, and to generate an image signal (i.e., form an image) from the sensed light. The image processing subsystem 24 is electrically connected to the detector 22, and is configured to receive the image signal from the detector 22, and to perform image analysis on the received image signal in order to determine the spatial configuration of the seam-lines 32. As used herein, the term “spatial configuration” refers to the arrangement of an object or feature in space, and includes at least the position (e.g., location or coordinates) and orientation (e.g., angular alignment or rotational attitude) of that object or feature relative to a defined reference frame. In the context of seam-lines within the optical structure 30, the spatial configuration may describe, for example, the location of a seam-line within the volume of the structure and the directional alignment of the seam-line with respect to internal geometric or optical reference features.

[0054] The display 29 may be electrically connected to the image processing subsystem 24 and / or the detector 22. The display 29, which may be implemented as any suitable image or video display device, is configured to display the image formed on the detector 22 and / or a processed version of the image (e.g., processed by the image processing subsystem 24).

[0055] The imaging lens 20 is specifically designed and configured to exclude all or practically all (in the claims “substantially all”) direct light from the light source 14 from reaching the detector 22, such that the scattered light 31 from the seam-lines forms a visible image on the detector 22 against a dark background. This may be achieved in part by providing the lens 20 with an annular light-transparent profile in which the inner part of the lens 20 is transparent and the outer part of the lens is opaque. In certain embodiments, the exclusion of direct light may be achieved by the imaging lens 20 blocking the direct light.

[0056] The separation between the optical structure 30 and the imaging lens 20 can be an important design consideration. In certain cases, if the distance is too short, light propagating unperturbed through the optical structure 30 may be collected by the imaging lens 20, potentially saturating the image formed by detector 22. To avoid this issue, certain embodiments maintain a minimum distance between the optical structure 30 and the imaging lens 20. This minimum distance may be a function of several factors, including, the geometry of the light source 14, the focal length of the collimating lens 16, and the aperture diameter (or equivalently the f-number) of the imaging lens 20. In particular, the minimum distance may be selected so that the following inequality holds: tan"1g) > tan’1g) where P is a geometric parameter of the source 14, F is the focal length of the lens 16, A is the aperture diameter of the lens 20, and u is the distance between the optical structure 30 and the lens 20. The specific parameter P may vary based on the geometry of the source 14. It is noted that decreasing the aperture diameter A may have the same or similar effect as increasing the distance between the optical structure 30 and the lens 20. By employing the combination of illumination arrangement 12 and imaging arrangement 18, the optical structure 30 is illuminated in a way that enhances visibility of the seam-lines 32 of the optical structure 30, thereby enabling precise and accurate determination of the spatial configuration (position, and preferably also orientation) of the seam-lines 32.

[0057] The system 10 according to the present disclosure is suitable for generating visible images of seam-lines in various types of optical structures. Such seam-lines are, as discussed above, generally formed at the intersection / interfacing of one or more internal surfaces of an optical structure with one or more external surfaces of the structure. For example, the present system 10 is applicable to beam-splitter cubes having internal beam-splitter surfaces that interface with external surfaces of the cube. It will be appreciated, however, that the system 10 is of particular advantageous when used for generating visible images of seam-lines in a light-guide optical element (LOE) as part of inspection and optical performance evaluation of the LOE. For context, a brief discussion of exemplary LOE architecture will now be provided. In general, an LOE is formed from a light-transmitting substrate having parallel major external surfaces that support propagation of light by internal reflection at these major external surfaces. Within the substrate, the LOE further includes one or more partially-reflecting internal surfaces that intersect the major external surfaces to form the aforementioned seam-lines. These internal surfaces often comprise one or more sets of mutually-parallel partially-reflecting surfaces configured to perform optical aperture expansion in one or more dimensions by redirecting the light propagating through the substrate into a deflection direction, and ultimately coupling a proportion of the propagating light out of the LOE toward the eye of a viewer. Detailed description of various LOE architectures can be found in numerous patent documents by Lumus Ltd. of Israel, such as, for example, US Patent No. 7,457,040, US Patent No. 10, 048,499, US Patent No. 10,551,544, and US Patent No. 11,543,583, the disclosures of which are incorporated herein by reference in their entirety for background purposes. By way of one non-limiting example of a suitable LOE, FIG. 2 illustrates an optical structure 30 implemented as an LOE similar to that described in US Patent No. 11,543,583, and configured for two-stage and two-dimensional optical aperture expansion. This exemplary LOE includes a pair of parallel major external surfaces 34a and 34b that support propagation of light by internal reflection at the major external surfaces 34a and 34b, and two sets of mutually-parallel partially-reflecting surfaces 36 and 38 that are internal to the LOE (i.e., located between the major external surfaces 34a and 34b). Collimated image illumination is generated by an image projector (not shown), and is injected into the LOE by an optical coupling-in configuration, such as a coupling reflector or coupling prism (also not shown). The internal surfaces 36 are located in a first region of the LOE and the internal surfaces 38 are located in a second region of the LOE. The internal surfaces 38 are obliquely inclined relative to the major external surfaces 34a and 34b, and the internal surfaces 36 have an orientation that is non-parallel to the internal surfaces 38. Accordingly, the collimated image illumination propagating by internal reflection between major external surfaces 34a and 34b in the first region of the LOE is progressively deflected by the internal surfaces 36 into the second region of the LOE, thereby performing optical aperture expansion in a first dimension. This deflected light continues propagating by internal reflection between the major external surfaces 34a and 34b and interacts with the internal surfaces 38, which progressively couple the light out of the LOE toward the eye of a viewer, thereby performing optical aperture expansion in a second dimension. In the illustrated LOE, each of the seam-lines 32 is precisely formed at the interface (or intersection) between two planes: one plane defined by an internal surface (e.g., 36 or 38), and the other plane defined a major external surface (e.g., 34a or 34b). It will be appreciated that the LOE may include additional sets of internal surfaces, for example additional parallel partially reflecting surfaces, and / or one or more planar beam-splitters, and / or a reflecting surface functioning as an optical coupling-in configuration.

[0058] FIG. 2 also shows the beam 17 impinging the LOE at the major external surface 34a, such that the beam 17 impinges the seam-lines 32 formed from the internal surfaces 36 and 38 at nonnormal angles of incidence. FIG. 3 illustrates the LOE of FIG. 2 from a different view, showing the beam 17 impinging the LOE at non-normal angles (85 degrees in the figure).

[0059] In general, the seam-lines 32 in the optical structure 30 are inconspicuous, meaning that they are not easily visible to the human eye, and are not visible when the optical structure is imaged using conventional illumination and imaging techniques. This is particularly true for the case of LOEs used in near eye displays (NEDs), where the LOEs are specifically designed and manufactured in a way that makes the interfaces between the internal partially-reflecting surfaces (e.g., 36 and 38) and the major external surfaces (e.g., 34a and 34b) as inconspicuous as possible, such that the formed seam-lines 32 are rendered practically invisible not only to the user of to the user of the NED, but also for external observers looking at the LOE from external viewpoints.

[0060] According to certain embodiments, the illumination 15 that is emitted by the light source 14 is symmetric about an axis normal to one of the major external surfaces 34a. This symmetric illumination, which in certain embodiments may be symmetric dark-field illumination, reduces or avoids shifts in the apparent location of the seam-lines 32 in the image formed on the detector 22. In one non-limiting implementation, the symmetric illumination is achieved by implementing the light source 14 as an annular source that emits an annular illumination pattern. The annular source may be implemented in various ways, including, for example, as LED ring lights, fiber optic ring lights, halogen or arc lamps with annular condensers, or any other suitable annular illumination configuration. In one embodiment, for example as illustrated in FIG. 4, the source 14 includes a reticle R having a transparent annular disk D. which may be positioned in the focal plane of the lens 16. The annular disk D has an inner diameter di and an outer diameter d2, and outputs the annular illumination pattern.

[0061] Other symmetric illumination techniques besides annular illumination are also envisaged, including, for example, dipole illumination (whereby the source 14 is a dipole source), rectangular- pattern illumination (whereby the source 14 is rectangular-shaped, for example LED lights arranged in a rectangular pattern), cross-pattern illumination (whereby the source 14 is crossshaped, for example LED lights arranged in a cross pattern), and others.

[0062] In the non-limiting embodiment illustrated in FIGS. 1 and 4, the light source 14 (implemented for example as a reticle R having transparent annular disk D) is placed at the focal plane of the collimating lens 16 (at focal distance F). The light 15 that is output (emitted) by the annular disk illuminates the optical structure 30 via the collimating lens 16 (as light 17), which is then imaged by the imaging arrangement 18. As mentioned previously, while FIG. 1 depicts the rays of the beam 17 as being parallel to the optical axis for illustrative purposes, this is not necessarily the case in practice. In the present embodiment, the light source 14 is specifically an annulus (annular disk) located at the focal plane of the collimating lens 16. Due to the annular shape, no light emanates on the optical axis. Instead, light is emitted only at oblique angles defined by the diameters di and d2 of the annulus and the focal length of the collimating lens 16. This off- axis emission inherently results in the rays of the beam 17 not being parallel to the optical axis. Furthermore, in this embodiment, the specific parameter P for the inequality for the minimum distance discussed above is di (the inner diameter of the annular disk D). As previously noted, the specific parameter P can vary based on the geometry of the source 14 and its resulting illumination pattern. For instance, in an embodiment utilizing a rectangular- shaped light source that generates a rectangular illumination pattern, the parameter P would be twice the distance from the center of the rectangle to the farthest point on the rectangle.

[0063] FIG. 5 illustrates an image 40, for example displayed by the display 29, of seam-lines of an LOE (such as the LOE of FIGS. 2 and 3) formed by the detector 22 using the optical setup illustrated in FIG. 1 and the source 14 illustrated in FIG. 4. Here, the annular illumination is imaged by the imaging arrangement 18 at the periphery of the image, and a junction of seam-lines 32 is clearly located at or near the center of the image. This clear imaging of the seam-lines 32 makes it relatively easy for the image processing subsystem 24 to perform image analysis, which may be achieved using computer vision techniques. In further detail, the image processing subsystem 24 may analyze the image to identify and track straight lines of the optical structure 30 and to differentiate the identified and tracked straight lines from the illumination. FIG. 6 illustrates the image 40 of FIG. 5, further showing a sample tracked line (approximately vertical seam-line in the center of the ring of FIG. 5) within a boundary box that demarcates a region of interest (ROI) defined by the image processing subsystem 24 software (e.g., defined by the computer vision software). The tracked seam-line is the physical seam-line in the optical structure / LOE. FIG. 6 also shows a reconstructed line, overlaid on the tracked line, that is generated / reconstructed by the image processing subsystem 24 in order to determine the spatial configuration of the tracked seam-line.

[0064] As mentioned above, the illumination, produced for example by an annular source or dipole source, is collimated to infinity (or approximately to infinity). One particular advantage of using an annular illumination (an annular source as the light source 14) is that if the annulus (e.g., annular disk) is not well collimated or if the inner diameter of the annulus is small such that part of the illumination enters the captured image, tracking of the lines within the image still remains relatively easy for the image processing subsystem 24. This is conveyed in FIGS. 7A and 7B, which shows some of the annular illumination in the image (as compared to FIG. 5), but the straight lines and their junction still readily tracked by the image processing subsystem 24. FIG. 7A shows the same tracked vertical line as in FIG. 6, and the line reconstructed by the image processing subsystem 24. FIG. 7B is an enlarged view of a region of the image of FIG. 7A, showing the junction between the following two seam-lines: 1) the vertical seam-line in the center of the ring of FIG. 5, and 2) the horizontal seam-line at a junction with that vertical seam-line. Also shown in FIG. 7B is a cross that indicates the tracked position of the junction (as tracked by the image processing subsystem 24).

[0065] FIGS. 8 A and 8B are a schematic representation of an optical simulation set-up of the system 10. In this optical simulation, the lenses 16 and 20 are implemented as paraxial lenses and the object to be imaged is a diffusing pattern 30’ (instead of optical structure 30), shown here as a cross-shaped pattern. FIGS. 9 - 11 illustrate images formed on the detector 22 for different simulation scenarios. For example, FIG. 9 shows a case where the source 14 is a thin annular source (i.e., has a large inner diameter di). Here, the imaging is only of the diffusing cross (i.e., only the diffusing pattern 30’ is visible in the image). When the inner diameter di of the annular source 14 is smaller (i.e., when the annular source is thicker), both the diffusing cross 30’ and the source 14 can be seen in the image, as shown in FIG. 10. Finally, if the illumination pattern is of a circle (no inner diameter of the annulus) the diffusing pattern 30’ is not visible in the image because the detector is blinded by the direct view of the source 14, as shown in FIG. 11.

[0066] Returning now to FIG. 1, in certain embodiments, a mounting arrangement 50, which may be implemented as a mechanical mount or holder, such as, for example, retaining rings, spring clips, brackets, and the like, may be used for holding the optical structure 30 in position between the illumination arrangement 12 and the imaging arrangement 18. In certain embodiments, the mounting arrangement 50 may include or may be mechanically connected to a spatial configuration adjustment mechanism 52, such as one or more gimbals, to allow for translationally moving, rotating, and / or tilting of the optical structure 30 relative to the collimating lens 16 (providing 5 DOF adjustment). This enables adjustment and / or refinement of the exposure angle(s) of the optical structure 30 relative to the collimating lens 16 as well as the option to change or adjust which seam-lines are exposed to the illumination from the light source 14. Consider, for example, when the optical structure is implemented as the LOE illustrated in FIG. 2. When the LOE assumes a first spatial configuration, the illumination and imaging may be such that a visible image of some of the seam-lines precisely formed at the intersection between the internal surfaces 36 and the major external surfaces 34a and 34b is formed on the detector, but the seam-lines precisely formed at the intersection between the internal surfaces 38 and the major external surfaces 34a and 34b are less visible in the formed image. Adjusting the position and / or orientation of the LOE so that the LOE assumes a second spatial configuration may enable the system to form a visible image of the seam-lines precisely formed at the intersection between the internal surfaces 38 and the major external surfaces 34a and 34b.

[0067] In certain embodiments, the spatial configuration adjustment mechanism 52 may be further configured to provide lateral adjustment so as to enable adjustment of the separation between the optical structure 30 and the imaging lens 20 in order to ensure that the optical structure 30 is positioned at least at the minimum distance from the imaging lens 20.

[0068] In certain embodiments, a movable mounting arrangement 60 may be used for holding the light source 14, and may be configured to move or adjust the position of the light source 14 relative to the optical structure 30, which may enable adjustment or refinement of the non-normal angles at which the light 17 impinges upon the seam-lines 32 of the optical structure 30. The light source 14 may be moved (via the mounting arrangement 60) based on, for example, the generated image of the seam-lines on the detector 22. For example, if the seam-line image is of low quality (e.g., the seam-lines are not bright enough, for example due to improper non-normal angle), the position of the light source 14 may be adjusted so as to adjust the non-normal angle (while monitoring the generated seam-line image), until the generated seam-line image is of sufficient quality (e.g., sufficient brightness). This provides a kind of image-quality feedback loop.

[0069] The quality of the seam-line image may also be adjusted by adjusting the f-number of the imaging lens 20. This may be accomplished by adjusting the size of the iris of the imaging arrangement 18, by using an aperture stop to control the entrance pupil of the lens 20. Adjustment of the f-number consequently adjusts the aperture diameter A of the lens 20, which as mentioned above may have the same or similar effect as increasing the distance between the optical structure 30 and the lens 20. In certain embodiments, the aperture diameter A and the separation between the optical structure 30 and the imaging lens 20 may be adjusted contemporaneously to prevent the imaging lens from collecting the aforementioned unperturbed light, and thus preventing saturation of the image.

[0070] In certain embodiments, the aforementioned adjustments may be manual adjustments, i.e., the adjustments may be performed manually by an operator of the system 10. In other embodiments, the adjustments may be automated and controlled adjustments, for example in response to control signals from a control subsystem (which may be part of, or electrically coupled to, the image processing subsystem).

[0071] Turning now to FIG. 12, there is shown a flow diagram of a process (method) for, among other things, imaging seam-lines 32 in an optical structure 30 using the system 10, according to embodiments of the present disclosure. Reference is also made to FIGS. 1 - 4.

[0072] At stage 1202, an optical structure, such as an LOE (e.g., the LOE illustrated in FIG. 2), is deployed in the optical path between the illumination arrangement 12 and the imaging arrangement 18.

[0073] At stage 1204, the light source 14 is actuated to emit light 15. In certain embodiments, the actuation of the light source 14 may be controlled by a computerized control subsystem (which may be part of, or electrically coupled to, the image processing subsystem 24).

[0074] At stage 1206, the emitted light 15 is received at the collimating lens 16, and an output beam 17 - that is collimated to infinity or approximately to infinity - is output from the collimating lens 16. The output beam 17 is directed toward the optical structure at non-normal angles, such that that the output beam 17 is scattered by the seam-lines 32.

[0075] At stage 1208, the scattered light 31 from the seam-lines 32 is received at the imaging lens 20. In this receiving stage, the imaging lens 20 substantially excludes direct light from the light source 14 from reaching the detector 22, such that at stage 1210, the detector 22 senses the scattered light received from the imaging lens 20 and generates an image signal from the sensed light such that the scattered light 31 from the seam-lines 32 forms a visible image against a substantially dark background.

[0076] At stage 1212, the image processing subsystem 24 may receive the image signal from the detector 22 and perform image analysis on the received image signal in order to determine the spatial configuration (at least one of position or orientation) of the seam-lines 32 in the optical structure 30.

[0077] Stages 1204 through 1212 may be repeated as necessary for inspection / analysis of the optical structure, for example while performing one or more of: moving, rotating, and / or tilting of the optical structure 30 relative to the collimating lens 16 (via mounting arrangement 50), adjusting the position of the light source 14 relative to the optical structure 30 (via mounting arrangement 60), and adjusting the f-number of the imaging lens 20.

[0078] It will be appreciated that the process 1200 may constitute a sub-process of a larger LOE assembly process, which can include various other stages and sub-stages, such as manufacturing stages (e.g., transparent plate coating, plate stacking and bonding, stack slicing, etc.), alignment stages, and optical performance evaluation stages.

[0079] The descriptions of the various embodiments of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

[0080] As used herein, the singular form, “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.

[0081] The word “exemplary” is used herein to mean “serving as an example, instance or illustration”. Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and / or to exclude the incorporation of features from other embodiments.

[0082] It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the disclosure. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0083] To the extent that the appended claims have been drafted without multiple dependencies, this has been done only to accommodate formal requirements in jurisdictions which do not allow such multiple dependencies. It should be noted that all possible combinations of features which would be implied by rendering the claims multiply dependent are explicitly envisaged and should be considered part of the disclosure.

[0084] Although the disclosure has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A system for generating an image of seam-lines in an optical structure, the system comprising: an illumination arrangement comprising: a light source for emitting light, and a collimating lens configured to receive light from the light source and to output an output beam, that is collimated to infinity or approximately to infinity, towards the optical structure, wherein the illumination arrangement is configured such that the output beam is directed toward the optical structure at non-normal angles so that that the output beam is scattered by the seam-lines, and wherein the seam-lines are formed at interfaces between internal components of the optical structure and optical surfaces of the optical structure; and an imaging arrangement comprising: an imaging lens configured to receive scattered light from the seam-lines of the optical structure, and a detector configured to sense light received from the imaging lens and to generate an image signal from the sensed light, wherein the imaging lens is configured to substantially exclude direct light from the light source from reaching the detector, such that the scattered light from the seam-lines forms a visible image on the detector against a substantially dark background.

2. The system of claim 1, further comprising an image processing subsystem configured to: receive the image signal from the detector, and perform image analysis on the received image signal in order to determine at least one of position or orientation of the seam-lines in the optical structure.

3. The system of claim 1, wherein the light source includes an annular light source.

4. The system of claim 1, wherein the light source includes a dipole source.

5. The system of claim 1 , wherein the light source comprises a reticle having a transparent annular disk.

6. The system of claim 1, wherein the light source is positioned at a focal plane of the collimating lens.

7. The system of claim 1, wherein the imaging lens has a transparent inner portion and an opaque external portion.

8. The system of claim 1, wherein the optical structure is a light-guide optical element having two major external surfaces and at least one internal surface deployed between the two major external surfaces, and wherein the seam-lines are formed at interfaces between the at least one internal surface and the two major external surfaces.

9. The system of claim 1, wherein the light emitted by the light source is symmetric around an axis normal to a major external surface of the optical structure.

10. The system of claim 1, wherein the light source is configured to emit light for dark- filed illumination.

11. A method for generating an image of seam-lines in an optical structure, the method comprising: emitting light from a light source; receiving the emitted light at a collimating lens and outputting an output beam from the collimating lens, wherein the output beam is collimated to infinity or approximately to infinity; directing the output beam toward the optical structure at non-normal angles, such that that the seam-lines scatter the output beam, wherein the seam-lines are formed at interfaces between internal components of the optical structure and optical surfaces of the optical structure; receiving scattered light from the seam-lines at an imaging lens, wherein receiving the scattered light by the imaging lens includes substantially excluding direct light from the light source from reaching a detector; and sensing the scattered light received from the imaging lens at the detector and generating an image signal from the sensed light, wherein the scattered light from the seam-lines forms a visible image against a substantially dark background.

12. The method of claim 11, further comprising: receiving, by an image processing subsystem, the image signal from the detector; and performing, by the image processing subsystem, image analysis on the received image signal in order to determine at least one of position or orientation of the seam-lines in the optical structure.

13. The method of claim 11, wherein the light source includes an annular light source.

14. The method of claim 11, wherein the light source includes a dipole source.

15. The method of claim 11, wherein the light source comprises a reticle having a transparent annular disk.

16. The method of claim 11, further comprising: deploying the light source and the collimating lens such that the light source is positioned at a focal plane of the collimating lens.

17. The method of claim 11, wherein the imaging lens has a transparent inner portion and an opaque external portion.

18. The method of claim 11, wherein the optical structure is a light-guide optical element having two major external surfaces and at least one internal surface deployed between the two major external surfaces, and wherein the seam-lines are formed at interfaces between the at least one internal surface and the two major external surfaces.

19. The method of claim 11, wherein the light emitted by the light source is symmetric around an axis normal to a major external surface of the optical structure.

20. The method of claim 11, wherein the light emitted by the light source is dark-field illumination.

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