Optical inspection system

Abstract

An inspection system is provided to inspect an array of optical plates having a plurality of mutually parallel reflective internal surfaces. The system comprises a scanning arrangement with an illumination source configured to emit a collimated source beam toward the array, and an optical angular detector configured to detect the angle of a return beam exiting the array. The inspection system is configured to scan the array by emitting the source beam, thereby defining a direct reflection path from the illumination source to the optical angular detector, the direct reflection path passing through the array and reflecting off an inspected one of the internal surfaces; and effecting a relative movement between the array and the scanning arrangement. The inspection system identifies optical inhomogeneities on the inspected internal surface based on one or more variations in the return beam measured by the optical angular detector.

Description

OPTICAL INSPECTION SYSTEMFIELD OF THE INVENTION

[0001] The presently disclosed subject matter relates to optical testing, and in particular to systems for non-contact measurement of internal reflective surfaces.BACKGROUND OF THE INVENTION

[0002] The process of manufacturing a lightguide optical element may include producing an intermediate work product comprising a plurality of optical plates which are stacked and attached with an adhesive to form an optical array. After the optical plates have been glued together, it may be desired to inspect the surface quality of the internal surfaces between the optical plates, for example to identify any defects which may adversely affect operation of the lightguide optical element.SUMMARY

[0003] According to an aspect of the presently disclosed subject matter, there is provided an inspection system configured to inspect an array of optical plates, the array comprising a plurality of mutually parallel partially reflective internal surfaces, the system comprising a scanning arrangement comprising an illumination source configured to emit a collimated source beam of light toward an entrance surface of the array, and an optical angular detector configured to detect the angle of a return beam of light exiting the array via an exit surface thereof; the inspection system being configured to scan the array by:operating the scanning arrangement to emit the source beam toward the entrance surface, thereby defining a direct reflection path from the illumination source to the optical angular detector, the direct reflection path passing through the array and reflecting off an inspected one of the internal surfaces; andeffecting a relative movement along a predetermined path between the array and at least a portion of the scanning arrangement during its operation;the inspection system being further configured to identify optical inhomogeneities on the inspected internal surface based on one or more variations in the return beam measured during the scanning by the optical angular detector.

[0004] The scanning arrangement may further comprise an illumination aperture through which the illumination source emits the source beam.

[0005] The scanning arrangement may further comprise a detector aperture through which the optical angular detector receives the return beam.

[0006] The inspection system may be further configured to maintain a fixed distance between the illumination aperture and the detector aperture during the scanning, the direct reflection path passing through both of the apertures.

[0007] The inspection system may be configured to selectively maintain one of a plurality of fixed distances between the illumination aperture and the detector aperture during scanning, wherein each of the plurality of fixed distances corresponds to a respective direct reflection path reflecting off a different inspected one of the internal surfaces.

[0008] The inspection system may further comprise a shifting arrangement configured to change the distance between the illumination aperture and the detector aperture.

[0009] The scanning arrangement may further comprise an illumination mask in which the illumination aperture is formed, and a detector mask in which the detector aperture is formed, the shifting arrangement being configured to move the illumination and / or the detector mask.

[0010] The scanning arrangement may further comprise a spatial light modulator having a pixelated surface configured to be operated to selectively impede transmission of light at each pixel of the pixelated surface, the inspection system being configured to operate the spatial light modulator to form the illumination aperture or the detector aperture.

[0011] The inspection system may be configured to operate the spatial light modulator to form the illumination aperture and the detector aperture.

[0012] The illumination source may be configured to emit the source light toward the entrance surface at a predefined oblique entrance angle, the direct reflection path being further defined by the entrance angle.

[0013] The inspection system may further comprise a translation arrangement configured to effect the relative movement between the array and at least a portion of the scanning arrangement.

[0014] The inspection system may be configured to simultaneously detect the angles of a plurality of return beams, each of the return beams corresponding to a respective direct reflection path reflecting off a different inspected one of the internal surfaces.

[0015] The illumination source may be configured to emit the source light toward the entrance surface at one of a plurality of oblique entrance angles, wherein each of the entrance angles defines a direct reflection path reflecting off a different inspected one of the internal surfaces.

[0016] The inspection system may be configured to identify an optical homogeneity when the angle of the return beam measured by the optical angular detector changes during scanning.

[0017] The optical angular detector may comprise optics configured to be focused at infinity.

[0018] The inspection system may further comprise one or more lightguide elements, each configured to redirect light toward or exiting the array.

[0019] The one or more lightguide elements may be prismatic.

[0020] A single surface of the array may constitute the entrance and exit surfaces thereof.

[0021] The inspection system may further comprise a coupling arrangement configured to mitigate effects of the surface quality of the entrance and / or exit surface.

[0022] The coupling arrangement may comprises:a coupling plate spaced from the entrance and / or exit surface of the array and having an entrance surface parallel thereto; andan index-matching material having an index of refraction substantially that of the array, the index-matching material substantially filling the space between the coupling plate and the entrance and / or exit surface of the array.

[0023] The index-matching material may be a liquid.

[0024] The scanning may comprise emitting the source beam toward at least one entrance surface of the array which is not parallel with the exit surface.

[0025] The surfaces of the optical plates may be partially reflective.

[0026] The optical angular detector may comprise a spectrometer, the inspection system being configured to identify optical inhomogeneities at each of a plurality of inspected internal surfaces based on variations in a corresponding spectral band of the return beam measured by the spectrometer.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0028] Fig. 1 schematically illustrates an optical structure comprising an array of optical plates;

[0029] Fig. 2 schematically illustrates an inspection system configured to identify defects on internal surfaces of the array illustrated in Fig. 1;

[0030] Fig.3 illustrates illumination and detector masks of the inspection system illustrated in Fig. 2;

[0031] Fig. 4 illustrates a modification of the of the inspection system illustrated in Fig. 2;

[0032] Fig. 5A illustrates a spatial light modulator according to examples of the inspection system illustrated in Fig. 2;

[0033] Figs.5B and 5C illustrate examples of the spatial light modulator illustrated in Fig. 5 A, operated to form apertures therein;

[0034] Fig. 6 illustrates a modification of the of the inspection system illustrated in Fig. 2;

[0035] Fig.7 illustrates a lightguide according to examples of the inspection system illustrated in Fig. 2; and

[0036] Figs. 8A and 8B illustrate a coupling arrangement according to examples of the inspection system illustrated in Fig. 2.DETAILED DESCRIPTION

[0037] The presently disclosed subject matter is directed toward an inspection system for identifying defects, for example optical inhomogeneities or other surface imperfections including, but not limited to, mis-parallelisms, exhibiting surface power, or any other irregularity which affects reflection of light therefrom, in internal surfaces of an optical structure. As illustrated in Fig. 1, the optical structure may comprise an array 10 of optical plates 12 bonded together at their surfaces. The bonded surfaces of the plates 12 constitute mutually parallel internal surfaces 14 of the array 10. According to some examples, each internal surface is coated, for example by coating all of the plates 12, by coating at least every alternate plate, etc.

[0038] According to some examples, the internal surfaces 14 are partially reflective, e.g., within a predetermined range of incident angles, for example determined, inter alia, by one or more coatings applied to the surfaces.

[0039] According to some examples, the array 10 is an intermediate work product in the manufacture of an optical lightguide assembly. However, it will be appreciated by way of example only, and the inspection system disclosed herein may be used to inspect optical structures produced for any purpose, mutatis mutandis.

[0040] As illustrated in Fig. 2, there is provided an inspection system, which is generally indicated at 100, configured to inspect internal surfaces 14 of an array 10 of optical plates 12, for example to identify optical inhomogeneities thereon. The inspection system 100 comprises a scanning arrangement 102 configured to scan an inspected internal surface 14i (i.e., the internal surface currently being inspected) of the array 10, and a translation arrangement configured to effect a relative movement between the array and at least a portion of the scanning arrangement, for example as indicated by arrow A. The inspection system 100 may further comprise a controller(not illustrated) configured to direct operation thereof, including its components. The controller may be further configured to analyze data collected by the inspection system, etc., for example as described below.

[0041] The scanning arrangement 102 is configured to scan the inspected internal surface 14i of the array 10 by detecting changes in the reflection of a beam impinging thereon. Accordingly, the scanning arrangement 102 is configured to emit a source beam Bsand measure the angle of a return beam Br, i.e., the source beam reflected off the inspected internal surface 14i, for example as described below.

[0042] According to some examples, the scanning arrangement 102 comprises an illumination source 106 configured to emit a collimated source beam of light, and to direct it toward an entrance surface Sin of the array. The illumination source 106 may be configured to direct the source beam such that it impinges on the entrance surface Sin at an oblique entrance angle which is within a predetermined range of angles, for example such that sufficient light of the source beam enters array 10 via the entrance surface and is reflected off the inspected internal surface 14i, and returns via an exit surface Sout.

[0043] In order to facilitate directing the source beam to an entrance location Lin of the entrance surface Sin, the scanning arrangement may further comprise an illumination aperture 108. According to some examples, the illumination aperture 108 may be provided as part of the illumination source 106, for example as is known in the art.

[0044] The scanning arrangement 102 may further comprise a detector, for example an optical angular detector 110, configured to detect the angle of the return beam. According to some examples, the entrance and exit surfaces Sin, Sout are the same surface of the array 10.

[0045] The optical angular detector 110 may comprise optics (not illustrated) configured to facilitate detecting the angle, for example a change in angle, of the return beam. As focusing optics converge parallel rays of light to a single point on a focal plane, the optics may be configured to be focused at infinity. Accordingly, the return beam will converge on the same point on the focal plane (e.g., a photosensitive sensor) of the optical angular detector 110 for a given angle thereof; if the return beam converges on a different point on the focal plane, it indicates a change in the angle of the return beam.

[0046] As the intensity of the return beam may be extremely low, in particular wherein a relatively large number of internal surfaces are disposed between the inspected internal surface 14i and the entrance and exit surfaces Sin, Sout, an optical angular detector 110 having sufficient sensitivity should be provided, corresponding to the anticipated intensity of the return beam based,e.g., on the geometry of the array, the intensity of the source beam provided by the illumination source 106, etc.

[0047] Similarly, the resolution of the optical angular detector 110 should be sufficient to facilitate identification by the inspection system 100 of optical inhomogeneities and / or other defects which are above a predetermined threshold, for example as described below.

[0048] As further seem in Fig. 2, as the source and return beams propagates through the array, it is partially reflected by each of the internal surfaces 14 it impinges upon, creating a plurality of beams (indicated at Bother,' only two of these other beams are illustrated in Fig. 2) which are reflected toward the exit surface Sout, each by a different one of the internal surfaces. Accordingly, the illumination source 106 may be configured to emit the source beam sufficiently collimated and narrow such that the beams which are reflected off the internal surfaces 14 of the array 10 are spaced from each other.

[0049] According to some examples, e.g., in order to facilitate isolating the return beam, the scanning arrangement may further comprise a detector aperture 112 may be provided. The detector aperture may facilitate avoiding detection by the optical angular detector 110 of beams reflected off internal surfaces 14 other than the inspected internal surface 14i, i.e., along other reflection paths. According to some examples, the detector aperture 112 may be provided as part of the optical angular detector 110, for example as is known in the art. The inspection system 100 may be configured to ensure that the detector aperture 112 is disposed in an optical path between an exit location Lout of the exit surface 14i and the optical angular detector 110.

[0050] As mentioned above, the translation arrangement is configured to effect a relative movement between the array 10 and at least a portion of the scanning arrangement 102, for example along a predetermined trajectory. According to some examples, the translation arrangement is configured to move the array 10, for example comprising a stage 114 as illustrated in Fig. 2. According to some examples (not illustrated), the translation arrangement is configured to move the scanning arrangement, for example without changing the relative locations of the illumination source 106 and the optical angular detector 110 with respect to each other, and without changing the angles thereof with respect to the array 10.

[0051] During scanning of the array 10, the illumination source 106 is operated to emit a source beam, for example via the illumination aperture 108, thereby defining a direct reflection path between the illumination source to the optical angular detector 110, for example via the detector aperture 112. The direct reflection path represents the trajectory that the source beam traverses from the illumination source 106 to the optical angular detector 110 through the array 10when reflected off the inspected internal surface 14i, and passes through the entrance and exit locations Ljn, Lout. It is defined, inter alia, by the entrance angle of the source beam at the entrance surface Sin, the refractive index of the material of the array, etc.

[0052] Furthermore, during scanning the translation arrangement is operated to effect a relative movement between the array 10 and at least a portion of the scanning arrangement 102. As described above, this may be accomplished, e.g., by moving the array or moving the scanning arrangement, or a portion thereof.

[0053] As the optical plates 12 of the array 10 are expected to be uniform throughout, and in particular as each of the internal surfaces 14 are expected to be optically homogeneous, i.e., each exhibiting uniform optical qualities across its entire area, the direct reflection path between the illumination source 106 and the optical angular detector 110 should not change when the array 10 is moved laterally relative to the scanning arrangement 102 along a path which is parallel to the surfaces 14.

[0054] During scanning, the optical angular detector 110 detects the return beam, which is expected to arrive along the downstream end of the direct reflection path, and measures the angle at which it arrives. According to some examples, the optical angular detector 110 measures the angle of the return beam relative to its focal plane. According to some examples, the optical angular detector 110 measures changes in the angle of the return beam during scanning.

[0055] Accordingly, the inspection system 10 is configured to identify optical inhomogeneities on the inspected internal surface 14i based on measurements by the optical angular detector 110 of the angle of the return beam during scanning. When the optical angular detector 110 measures a change in the angle of the return beam, an optical inhomogeneity is detected at the point on the inspected internal surface 14i where the source beam is reflected.

[0056] It will be appreciated that while a one-dimensional scan along the x-axis (as indicated by the coordinate system icon in Fig. 2) has been described above, this is by way of explanation only, and is not to be construed as limiting. In practice, the array 10 typically extends along the z-axis, the figures thus illustrating a schematic cross-section taken along the xy-plane. Accordingly, the inspection system 10 may be configured to inspect two-dimensional internal surfaces, e.g., by scanning along the x-axis as described above, then moving the scanning arrangement 102 and / or array 10 along the z-axis and repeating the scan. This may be repeated until some or substantially all of each of the internal surfaces 14 have been scanned in two dimensions, mutatis mutandis. This applies, mutatis mutandis, to each of the other examples described herein.

[0057] In addition, it will be appreciated that while the description of the inspection system 10 implies identification of local defects on the inspected internal surface, this is by way of example. The inspection system 10 may be further configured to identify if an inspected internal surface is parallel to the other internal surfaces 14 of the array 10, for example if the optical angular detector 110 measures the angle of the return beam reflected off one of the internal surfaces as being different than that of return beams reflected off other reflected surfaces, mutatis mutandis.

[0058] According to some examples, in order to prevent coherent summation of different reflection paths of rays that are off internal surfaces 14 other than the inspected internal surface 14i, i.e., along other reflection paths, the illumination source 106 may be configured to emit a source beam having a coherence length which is lower than the variance in the thicknesses of the optical plates 12 of the array 10. According to some examples, the illumination source 106 may comprise a broadband source.

[0059] According to some examples, the effect of noise from ghost reflections (i.e., secondary, tertiary, etc.; while typically only the secondary reflections have a measurable effect on the inspection, the term “ghost reflections” is used herein for completeness to include all reflections besides the primary reflection, i.e., the signal) may be reduced by selection of properties of the source light. As the intensity of the primary reflection is proportional to the reflectance R of the emitted light by the internal surfaces 14 of the array 10, and the intensity of the ghost reflections is proportional to the cube of the reflectance (i.e., A3) of the emitted light by the internal surfaces, the signal-to-noise ratio is inversely proportional to A2; lowering reflectance results in a higher signal-to-noise ratio. Accordingly, the illumination source may be configured to reduce the reflectance R of the emitted light by the internal surfaces by, e.g., selecting a suitable polarization, wavelength, and / or angle of the emitted light, for example as is known in the art, while ensuring that the intensity of the return beam Bris sufficient to allow detection thereof by the optical angular detector 110.

[0060] According to some examples, reflection of the source beam by the entrance surface Sin may be reduced by mechanical means, operating the illumination source to emit p-polarized light, impinging thereon at Brewster’s angle, etc. According to some examples, the entrance surface Sin may be inspected for inhomogeneities and / or other defects by operating the illumination source to emit s-polarized light

[0061] As illustrated in Fig. 3, in which only a top optical plate 12 of the array is illustrated, according to some examples the inspection system 10 comprises an illumination mask 116, e.g., separate from the illumination source 106, in which the illumination aperture 108 is formed.Similarly, according to some examples the inspection system 10 comprises a detector mask 118, e.g., separate from the optical angular detector 110, in which the detector aperture 112 is formed.

[0062] According to further examples, the inspection system 10 may comprise a shifting arrangement, schematically illustrated and indicated at 120, configured to change the fixed distance between the illumination and detector apertures 108, 112, e.g., by moving the illumination and / or detector mask 116, 118. Accordingly, the inspection system 10 may be configured to operate the shifting arrangement to change the change the position of the detector aperture 112 relative to the illumination aperture 108 to selectively align the detector aperture with a beam reflected off a selected one the internal surfaces 14, thereby facilitating selecting an internal surface for inspection.

[0063] As illustrated in Fig. 4, according to some examples the illumination source 106 is configured to produce a beam which is of a larger diameter than that of the illumination aperture 108. Accordingly, the diameter of the source beam may be determined by the size of the illumination aperture 108. Analogously, the inspection system 10 may be configured to position the detector aperture 112 to facilitate isolating the return beam from beams which are reflected from internal surfaces other than the one being inspected, for example as described above. According to some examples, the diameter of the detector aperture 112 is somewhat larger than the size of the return beam, such that in the event that it deviates from the direct reflection path, it will still pass therethrough to the optical angular detector 110 for measurement of the extent of the deviation. Accordingly, the translation arrangement may configured to move the illumination aperture and detector apertures 108, 112, thereby effecting the relative movement between the array 10 and a portion of the scanning arrangement 102.

[0064] According to examples in which the inspection system 10 comprises illumination and detector apertures 108, 112, the inspection system may be configured to maintain a fixed distance therebetween, such that the direct reflection path passes through both.

[0065] According to some examples, for example as illustrated in Figs. 5A and 5B, the illumination and / or detector mask 116, 118 may comprise a spatial light modulator 122 having a pixelated surface 124 comprising a plurality of pixels 126, for example in a grid pattern. The spatial light modulator 122 is configured to be operated to selectively and independently control each of the pixels 126 to either impede or allow transmission of light through the pixelated surface at its respective pixel location. According to some examples, the spatial light modulator 122 is electrically addressed, thereby facilitating operation thereby by the controller, and the controlleris configured to operate the spatial light modulator 122 to form the illumination and / or detector aperture 108, 112.

[0066] As illustrated in Fig. 5C, according to some examples a single spatial light modulator 122 may be provided, and operated to form the illumination aperture 108 and the detector aperture 112 therein, thereby providing both the illumination mask 116 and the detector mask 118.

[0067] According to some examples, the spatial light modulator 122 may, inter alia, constitute the shifting arrangement 120, for example by being operated to change the location of the detector aperture 112.

[0068] As illustrated in Fig. 6, the inspection system 10 may be configured to simultaneously detect the angles of a plurality of return beams, thereby facilitating inspection of several internal surfaces at the same time. According to some examples, the optical angular detector 110 may be configured to detect a plurality of return beams, each of which corresponds to a direct reflection path which is defined, inter alia, by the reflection off a respective one of the internal surfaces 14. The inspection system 10 may be configured such that each of the direct reflection paths is defined between the illumination source 106 and a different point on the focal plane of the optical angular detector 110, thereby facilitating differentiation between the different return beams. Accordingly, the inspection system 10 may be configured to inspect multiple inspected internal surfaces 14i with a single source beam.

[0069] As illustrated in Fig. 7, the inspection system 10 may comprise a lightguide element 128, or other suitable prismatic element, at least partially defining an optical path for the source beam between the illumination source 106 and the array 10. This may facilitate, e.g., providing the illumination source 106 in a more convenient location, preventing the illumination mask 116 from overlapping with the detector aperture 112 and vice versa (for example wherein the inspected internal surface 14i is close to the exit surface Sout. According to some examples (not illustrated), a similar lightguide element may be provided at least partially defining an optical path for the return beam between the array 10 and the optical angular detector 110, mutatis mutandis.

[0070] As illustrated in Fig. 8 A, the inspection system 10 may further comprise a coupling arrangement, which is generally indicated at 130, configured to mitigate effects of the surface quality of the entrance surface Sin on, e.g., the trajectory of the source beam. This is accomplished, inter alia, by providing a surface of a known quality for coupling in the source beam.

[0071] According to some examples, the coupling arrangement 130 comprises a coupling plate 132 spaced from the entrance surface Sin of the array 10. The coupling plate 132 has a smooth outer surface 134 configured to be parallel to the surfaces 14 of the array 10 during scanning.According to some examples, the coupling plate 132 has substantially the same refractive index as the optical plates 12 of the array 10. The coupling arrangement 130 may further comprise an indexmatching material 136, e.g., comprising a suitable liquid, substantially filling the space between the coupling plate 132 and the entrance surface Sin of the array 10. The index -matching material has a refractive index which is substantially the same as that of the optical plates 12 of the array 10, and as the coupling plate 132.

[0072] Refractive indices of different materials may be considered to be “substantially” the same if any mismatch therebetween is sufficiently small that its effect on identifying optical inhomogeneities and / or other defects is within a tolerable level, for example based on the requirements of the user.

[0073] The coupling arrangement 130 thus provides an entrance surface, i.e., the outer surface 134 of the coupling plate 132 which may be known to be substantially defect-free, and a medium, i.e., the index-matching material 136, which facilitates passage of the source beam from the coupling plate to the array 10 via the entrance surface Sin while substantially eliminating reflection and refraction thereof.

[0074] According to some examples, as illustrated in Fig. 8B, the coupling arrangement 130 may facilitate inspecting portions of an inspected internal surface 14i which are close to the edge of the array 10, by providing an optical path via an auxiliary entrance surface Sin' side of the array, for example at an exterior surface of the array which is perpendicular to the entrance surface Sin. The coupling arrangement 130 allows the source beam entering the array 10 via the auxiliary entrance surface Sin' to impinge upon the inspected internal surface 14i at the same angle as it would have had it entered the array 10 via the entrance surface Sin- 10075] It will be appreciated that while the coupling arrangement 130 is described herein with reference to and is illustrated in Figs. 8A and 8B in connection with the entrance of the source beam into the array 10, it may be similarly employed to mitigate effects of the surface quality of the exit surface Som on, e.g., the trajectory of the return beam, mutatis mutandis.

[0076] It will be appreciated that while the direct reflection path is described herein the specification and appended claims as representing or following the trajectory that the source beam traverses, inter alia, when reflected off the inspected internal surface, this is imprecise. In actuality, the direct reflection path represents / follows the traj ectory that the source beam traverses, inter alia, when reflected off an optically homogeneous reference inspected internal surface, i.e., an ideal reference surface which is similar to the actual inspected internal surface but free of optical inhomogeneities and / or other defects which are identified by the inspection system 10 as describedherein. However, as one having skill in the art is not expected to interpret this phrase with excessive pedantry, the abbreviated phrasing is used herein the specification and appended claims to increase readability to refer to such a reference surface.

[0077] It will be further appreciated that while the inspection system disclosed herein and recited in the appended claims is described in connection with to an array of optical plates comprising a plurality of mutually parallel reflective internal surfaces, this is for reference only, and should not be construed as limiting. In practice, the scope of the presently disclosed subject matter may extend to inspection systems configured to inspect other structures having sufficiently similar optical properties so as to allow inspection by the system as described herein and as recited in the appended claims, mutatis mutandis.

[0078] While the term “controller” is used herein the specification and appended claims with reference to a single element, it may comprise a combination of elements, which may or may not be in physical proximity to one another, without departing from the scope of the presently disclosed subject matter, mutatis mutandis. In addition, disclosure herein (including recitation in the appended claims) of a controller carrying out, being configured to carry out, or other similar language, implicitly includes other elements of the system carrying out, being configured to carry out those functions without departing from the scope of the presently disclosed subject matter, mutatis mutandis.

[0079] Herein the specification and appended claims, the term “source beam” is used to refer to light which traverses along the direct reflection path upstream of the inspected internal surface, and the term “return beam” is used to refer to light which traverses along the direct reflection path downstream of the inspected internal surface, or which deviates therefrom owing to an optical inhomogeneities on the inspected internal surface.

[0080] It will be recognized that examples, embodiments, modifications, options, etc., described herein are to be construed as inclusive and non-limiting, i.e., two or more examples, etc., described separately herein are not to be construed as being mutually exclusive of one another or in any other way limiting, unless such is explicitly stated and / or is otherwise clear. Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations, and modifications can be made without departing from the scope of the presently disclosed subject matter, mutatis mutandis.

Claims

CLAIMS1. An inspection system configured to inspect an array of optical plates, the array comprising a plurality of mutually parallel reflective internal surfaces, the system comprising a scanning arrangement comprising an illumination source configured to emit a collimated source beam of light toward an entrance surface of the array, and an optical angular detector configured to detect the angle of a return beam of light exiting the array via an exit surface thereof; the inspection system being configured to scan the array by:operating the scanning arrangement to emit the source beam toward the entrance surface, thereby defining a direct reflection path from the illumination source to the optical angular detector, the direct reflection path passing through the array and reflecting off an inspected one of the internal surfaces; andeffecting a relative movement along a predetermined path between the array and at least a portion of the scanning arrangement during its operation;the inspection system being further configured to identify optical inhomogeneities on the inspected internal surface based on one or more variations in the return beam measured during the scanning by the optical angular detector.

2. The inspection system according to claim 1, the scanning arrangement further comprising an illumination aperture through which the illumination source emits the source beam.

3. The inspection system according to claim 2, the scanning arrangement further comprising a detector aperture through which the optical angular detector receives the return beam.

4. The inspection system according to claim 3, being further configured to maintain a fixed distance between the illumination aperture and the detector aperture during the scanning, the direct reflection path passing through both of the apertures.

5. The inspection system according to claim 4, being configured to selectively maintain one of a plurality of fixed distances between the illumination aperture and the detector aperture during scanning, wherein each of the plurality of fixed distances corresponds to a respective direct reflection path reflecting off a different inspected one of the internal surfaces.

6. The inspection system according to any one of claims 3 through 5, further comprising a shifting arrangement configured to change the distance between the illumination aperture and the detector aperture.

7. The inspection system according to claim 6, the scanning arrangement further comprising an illumination mask in which the illumination aperture is formed, and a detector mask in which thedetector aperture is formed, the shifting arrangement being configured to move the illumination and / or the detector mask.

8. The inspection system according to any one of claims 3 through 7, the scanning arrangement further comprising a spatial light modulator having a pixelated surface configured to be operated to selectively impede transmission of light at each pixel of the pixelated surface, the inspection system being configured to operate the spatial light modulator to form the illumination aperture or the detector aperture.

9. The inspection system according to claim 8, being configured to operate the spatial light modulator to form the illumination aperture and the detector aperture.

10. The inspection system according to any one of the preceding claims, the illumination source being configured to emit the source light toward the entrance surface at a predefined oblique entrance angle, the direct reflection path being further defined by the entrance angle.

11. The inspection system according to any one of the preceding claims, further comprising a translation arrangement configured to effect the relative movement between the array and at least a portion of the scanning arrangement.

12. The inspection system according to any one of the preceding claims, being configured to simultaneously detect the angles of a plurality of return beams, each of the return beams corresponding to a respective direct reflection path reflecting off a different inspected one of the internal surfaces.

13. The inspection system according to any one of the preceding claims, the illumination source being configured to emit the source light toward the entrance surface at one of a plurality of oblique entrance angles, wherein each of the entrance angles defines a direct reflection path reflecting off a different inspected one of the internal surfaces.

14. The inspection system according to any one of the preceding claims, being configured to identify an optical homogeneity when the angle of the return beam measured by the optical angular detector changes during scanning.

15. The inspection system according to any one of the preceding claims, the optical angular detector comprising optics configured to be focused at infinity.

16. The inspection system according to any one of the preceding claims, further comprising one or more lightguide elements, each configured to redirect light toward or exiting the array.

17. The inspection system according to claim 16, wherein the one or more lightguide elements are prismatic.

18. The inspection system according to any one of the preceding claims, wherein a single surface of the array constitutes the entrance and exit surfaces thereof.

19. The inspection system according to any one of the preceding claims, further comprising a coupling arrangement configured to mitigate effects of the surface quality of the entrance and / or exit surface.

20. The inspection system according to claim 19, wherein the coupling arrangement comprises:a coupling plate spaced from the entrance and / or exit surface of the array and having an entrance surface parallel thereto; andan index-matching material having an index of refraction substantially that of the array, the index-matching material substantially filling the space between the coupling plate and the entrance and / or exit surface of the array.

21. The inspection system according to claim 20, wherein the index-matching material is a liquid.

22. The inspection system according to any one of claims 19 through 21, wherein the scanning comprises emitting the source beam toward at least one entrance surface of the array which is not parallel with the exit surface.

23. The inspection system according to any one of the preceding claims, wherein the surfaces of the optical plates are partially reflective.

24. The inspection system according to any one of the preceding claims, wherein the optical angular detector comprises a spectrometer, the inspection system being configured to identify optical inhomogeneities at each of a plurality of inspected internal surfaces based on variations in a corresponding spectral band of the return beam measured by the spectrometer.

25. The inspection system according to claim 3, the scanning arrangement further comprising a spatial light modulator having a pixelated surface configured to be operated to selectively impede transmission of light at each pixel of the pixelated surface, the inspection system being configured to operate the spatial light modulator to form the illumination aperture or the detector aperture.

26. The inspection system according to claim 25, being configured to operate the spatial light modulator to form the illumination aperture and the detector aperture.

27. The inspection system according to claim 1, the illumination source being configured to emit the source light toward the entrance surface at a predefined oblique entrance angle, the direct reflection path being further defined by the entrance angle.

28. The inspection system according to claim 1, further comprising a translation arrangement configured to effect the relative movement between the array and at least a portion of the scanning arrangement.

29. The inspection system according to claim 1, being configured to simultaneously detect the angles of a plurality of return beams, each of the return beams corresponding to a respective direct reflection path reflecting off a different inspected one of the internal surfaces.

30. The inspection system according to claim 1, the illumination source being configured to emit the source light toward the entrance surface at one of a plurality of oblique entrance angles, wherein each of the entrance angles defines a direct reflection path reflecting off a different inspected one of the internal surfaces.

31. The inspection system according to claim 1, being configured to identify an optical homogeneity when the angle of the return beam measured by the optical angular detector changes during scanning.

32. The inspection system according to claim 1, the optical angular detector comprising optics configured to be focused at infinity.

33. The inspection system according to claim 1, further comprising one or more lightguide elements, each configured to redirect light toward or exiting the array.

34. The inspection system according to claim 33, wherein the one or more lightguide elements are prismatic.

35. The inspection system according to claim 1, wherein a single surface of the array constitutes the entrance and exit surfaces thereof.

36. The inspection system according to claim 1, further comprising a coupling arrangement configured to mitigate effects of the surface quality of the entrance and / or exit surface.

37. The inspection system according to claim 36, wherein the coupling arrangement comprises:a coupling plate spaced from the entrance and / or exit surface of the array and having an entrance surface parallel thereto; andan index-matching material having an index of refraction substantially that of the array, the index-matching material substantially filling the space between the coupling plate and the entrance and / or exit surface of the array.

38. The inspection system according to claim 37, wherein the index -matching material is a liquid.

39. The inspection system according to any one of claims 36 through 38, wherein the scanning comprises emitting the source beam toward at least one entrance surface of the array which is not parallel with the exit surface.

40. The inspection system according to claim 1, wherein the surfaces of the optical plates are partially reflective.

41. The inspection system according to a claim 1, wherein the optical angular detector comprises a spectrometer, the inspection system being configured to identify optical inhomogeneities at each of a plurality of inspected internal surfaces based on variations in a corresponding spectral band of the return beam measured by the spectrometer.

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