System and method for testing a grating

Abstract

The present disclosure relates to systems and methods for testing gratings. Gratings, such as those used in waveguide displays, can have a large aspect ratio. For example, grating characteristics (e.g., period, feature size, etc.) can be much smaller than the grating area. Variations in grating characteristics across the grating area can appear like a secondary grating with a long grating period superimposed on the primary grating for which the grating was designed. Because the variations leading to the secondary grating occur over a long distance relative to the primary grating period, it can be difficult to locate and characterize these variations with testing methods designed for shorter distances. The present disclosure proposes systems and methods for quickly and efficiently detecting and characterizing secondary gratings.

Description

Technical Field

[0001] This disclosure relates to gratings, and more specifically to systems and methods for characterizing deviations from an ideal grating, the deviations occurring spatially in a region relatively large compared to the grating period. Background Technology

[0002] Gratings can be used to guide and manipulate light in imaging systems. For example, gratings can be used in waveguide displays to guide and project images from the display onto the user's eyes. When any or all of these gratings deviate from their design specifications, artifacts can be observed in the image from the display. Summary of the Invention

[0003] In at least one aspect, this disclosure generally describes a method for testing a grating. The method includes: directing light from a laser to a first test region on the grating; and capturing a grating image based on the light passing through the first test region. The method further includes analyzing the grating image to measure diffraction from a secondary grating and determining characteristics of the secondary grating from the diffraction when the measured diffraction is non-zero. The secondary grating may be generated by defects in a primary grating. The method also includes: directing light to a second test region; capturing a grating image from the second test region; and analyzing the grating image corresponding to the second test region to characterize defects in the primary grating and / or the system (e.g., substrate, coating).

[0004] In another aspect, this disclosure generally describes a system for testing gratings. The system includes a substrate, a laser, a camera, and a processor. The substrate of the system includes a primary grating in a primary grating region. The laser of the system is configured to project light of a test wavelength not diffracted by the primary grating onto a test region within the primary grating region. The camera of the system is configured to capture a grating image of the light after it has passed through the test region. The processor of the system is configured by software instructions to detect diffraction orders in the grating image, the diffraction orders corresponding to diffraction from a secondary grating having a period greater than that of the primary grating. The processor is further configured by software instructions to analyze the diffraction orders to determine the characteristics of the secondary grating.

[0005] In another aspect, this disclosure generally describes a method for testing a waveguide display. The method includes sequentially guiding light from a laser to a plurality of different test regions on a primary grating of the waveguide display. The guided light is at a test wavelength that is larger (i.e., longer than) the period of the primary grating, such that the light is not diffracted by the primary grating. The method also includes sequentially capturing grating images of the light after it has passed through each of the plurality of different test regions. The method further includes detecting the diffraction order of one or more of the captured grating images. The detected diffraction order corresponds to a secondary grating. Therefore, the method also includes analyzing the diffraction order to determine the characteristics of the secondary grating in each test region corresponding to each of the one or more grating images including the diffraction order.

[0006] The foregoing illustrative overview and other exemplary purposes and / or advantages of this disclosure, as well as the ways in which these purposes and / or advantages are achieved, are further explained in the following detailed description and its accompanying drawings. Attached Figure Description

[0007] Figure 1 A waveguide display according to a possible embodiment of the present disclosure is illustrated graphically.

[0008] Figure 2 It is a diagram. Figure 1 k-space diagram of the possible effects of gratings in waveguide displays.

[0009] Figure 3 It is a diagram. Figure 1 k-space plot of the effect of grating variation in waveguide display.

[0010] Figure 4 It corresponds to Figure 3 Example image of the k-space graph.

[0011] Figure 5 This is a k-space diagram illustrating a test of a grating according to a possible embodiment of the present disclosure.

[0012] Figures 6A to 6C The illustration shows a system for testing a grating according to a possible embodiment of the present disclosure.

[0013] Figure 7 It is by Figure 6C An example of a raster image captured by a raster testing system.

[0014] Figure 8 This is a flowchart of a method for testing a grating according to an embodiment of the present disclosure.

[0015] The components in the accompanying drawings are not necessarily drawn to scale relative to each other. In several views, the same reference numerals refer to corresponding parts. Detailed Implementation

[0016] This disclosure describes methods and systems for testing gratings (i.e., gratings). A grating is a spatially periodic structure that can diffract light when the spatial wavelength of the periodic structure approximates the optical wavelength of light. For example, wavelength-dependent diffraction can be used to direct light of certain wavelengths in certain directions, which can be used in a variety of applications (e.g., imaging, spectroscopy, etc.). A grating can reflect diffracted light (i.e., a reflective grating) or transmit diffracted light (i.e., a transmissive grating). Gratings can be formed in various ways. A substrate can be imprinted to form a grating. Material can be added (i.e., deposited) to or subtracted (e.g., etched) from a substrate to form a grating (e.g., a blazed grating). The optical properties (e.g., refractive index) of a substrate or coating (e.g., a photosensitive polymer film) can be altered by exposure to light to form a grating (e.g., a holographic grating). While the disclosed techniques can be used for all of the above-described gratings, specific applications (i.e., waveguide displays) will be described in detail. While specific applications will help explain the disclosed methods and systems and place them in the context of particularly useful examples, the disclosed techniques can be used in other applications (e.g., variants of the disclosed waveguide displays) and are generally applied more broadly to gratings.

[0017] A grating can be included in a waveguide display used in head-up displays such as augmented reality (AR) devices or virtual reality (VR) devices. The waveguide display is configured to project an image from the display onto a user's eyes. For example, AR glasses (i.e., smart glasses) can utilize a waveguide display, which includes an input coupling grating (i.e., an IC grating) to couple light from the display into a waveguide (e.g., a glass plate), where the light can be guided by total internal reflection (i.e., TIR) along the dimensions of the waveguide until the light interacts with an output coupling grating (i.e., an OC grating), which is configured to couple light exiting the waveguide and entering free space such that the light can be focused by the user's eyes for observation. In some embodiments, the waveguide display also includes an exit pupil expander grating (i.e., an EPE grating) positioned between the IC grating and the OC grating and configured to provide optical amplification and / or chromaticity adjustment of the guided light.

[0018] Gratings used in waveguide displays can include spatially periodic refractive indices (i.e., spatially varying refractive indices). Spatially varying refractive indices can be generated by material variations (e.g., crosslinking) and / or physical variations (e.g., thickness) in a film disposed on the surface of the waveguide or within the waveguide itself. For example, spatially varying refractive indices can be formed in a photoreactive film using holography (i.e., a holographic grating). Alternatively, spatially varying refractive indices can be generated by creating thickness variations in the film or waveguide. Thickness variations can include adding material to the film or waveguide (e.g., a subtractive surface-roughened grating, a nanolithography (printed) grating) or removing material from the film or waveguide. Spatially varying refractive indices can be discrete or continuous and can be described at least in part by the grating period, fill factor, feature size, and / or feature shape.

[0019] While this disclosure is not limited to any particular grating embodiment, a periodic binary grating (i.e., a binary grating) is described to illustrate specific principles. A binary grating may include refractive indices alternating between two refractive index values ​​over a grating period. The grating period of the binary grating may correspond to the length required for the transition between the two refractive index values. The fill factor of the binary grating may correspond to a percentage of the grating period specified for one of the two refractive index values. The feature size of the binary grating may correspond to the size of one of the two refractive index values ​​over the grating period.

[0020] Gratings used in waveguide displays can have large aspect ratios. For example, the grating period (Λ) can be less than 500 nanometers (nm), such as in the range of 100 nm to 400 nm (i.e., 100 nm ≤ Λ ≤ 400 nm), and the feature size can be in the range of 5 nm to 300 nm (e.g., 15 nm), while the grating itself can extend over a much larger area. For example, each side of the grating can have a length in the range of 1 cm to 3 cm.

[0021] Using actual manufacturing and / or replication techniques, it may be difficult to produce accurate grating parameters across the entire area of ​​the grating (i.e., the grating region). For example, variations may exist along the length of the grating in the grating's period, fill factor, feature size, feature shape, refractive index, or other properties. These variations can cause artifacts in the image projected by a waveguide display. For example, when viewed by a user's eye, these variations may produce a blurred or duplicated (i.e., ghosting) version of the displayed image. While artifacts themselves indicate variations in the grating, it may be difficult to easily determine the magnitude of the variation, the number of variations, and / or the location (or multiple locations) of the variations (or variations).

[0022] Inspection of gratings can be limited to small-scale visual inspection using microscopes such as scanning electron microscopy (SEM) or atomic force microscopy (AFM). While these techniques can characterize gratings at scales comparable to the grating's period (e.g., scale ≤ 5µm), characterizing large-scale changes (e.g., scale > 100µm) may be impractical due to the time required to inspect large areas (e.g., the entire grating) and / or the problems associated with stitching together local inspection areas. This disclosure describes a system and method for addressing this technical problem by rapidly and efficiently characterizing changes in gratings, enabling routine analysis of large areas (e.g., the entire grating). The disclosed solution can provide a means for inspecting gratings in a production environment, enabling rapid defect detection and allowing appropriate mitigation steps to be taken.

[0023] Figure 1 A waveguide display system (i.e., a system) according to a possible embodiment of the present disclosure is illustrated graphically. System 100 includes a display 110 configured to generate images (e.g., text, video, photographs, graphics, etc.) for display to a user. Display 110 may be an electronic display, such as an organic light-emitting diode (OLED) display. The system also includes a waveguide 130 that may be configured to receive display light 115 from display 110. Waveguide 130 may also be configured to guide display light 115 along a guiding portion 170 of the waveguide based on total internal reflection. Thus, waveguide 130 may have a wavelength suitable for visible wavelengths (e.g., 400 nm ≤ λ). o ≤700nm) and / or near-infrared wavelengths (e.g., 750nm≤λ) o The waveguide 130 is made of a material (e.g., glass) with a refractive index (e.g., 1.5 to 2.7) and dimensions (e.g., 150 μm ≤ thickness ≤ 10 mm) that allows total internal reflection (≤ 900 nm). The waveguide 130 can also be configured to output the projected light 125 to the user's eye 120. Therefore, the waveguide 130 can be positioned in front of the user's eye 120 and can be transparent at visible wavelengths, allowing the user to see an image superimposed on the user's view through the waveguide 130 from the display 110.

[0024] Waveguide 130 may utilize one or more gratings (i.e., gratings) to achieve the aforementioned functions. Each of the gratings may exist on a grating region within the waveguide. The gratings may be configured to redirect light along a specific angle. For example, waveguide 130 may include an IC grating 140 to redirect display light 115 from a first angle (e.g., aligned with surface normal vector 127) to a second angle greater than the critical angle for total internal reflection at the interface between waveguide 130 and the environment (e.g., air). Waveguide 130 may also include an EPE grating 160 disposed in the guide portion 170 of waveguide 130. EPE grating 160 may be configured to process light to facilitate image observation. For example, EPE grating may be configured to expand the exit pupil of waveguide 130 so that the display image can be observed within the viewing angle of eye 120. Waveguide 130 may also include an OC grating 150 configured to redirect guide light from a second angle greater than the critical angle of TIR to a third angle less than the critical angle of TIR, causing the projected light 125 to exit the waveguide 130. For example, the projected light exiting the waveguide may be perpendicular to the surface of the waveguide 130 (i.e., aligned with the surface normal vector 127) and in a direction toward the user's eye 120, such that when focused by the eye 120, the image of the display is focused on the user's retina. When there are no defects in the grating of the waveguide 130 (e.g., variations in grating period and / or feature size), the focused image can closely match the displayed image. In other words, any artifacts in the grating can degrade the imaging quality (e.g., resolution) of the system 100.

[0025] Although Figure 1 System 100 can be configured for monochromatic light, but it should be understood that the principles described for this monochromatic system can be adapted to colored (i.e., RGB) light. For example, one or more channels of light from display 110 (i.e., red (R), green (G), blue (B)) can be processed (e.g., routed) by one or more waveguides for the user's eye 120 to focus.

[0026] Figure 2 The grating shown in the diagram is used for propagation. Figure 1 A k-space diagram 200 illustrates the effect of light on the waveguide display. This diagram has two dimensions corresponding to the plane (x, y) of waveguide 130. The diagram includes multiple k-vectors. Each k-vector illustrates the redirection of light passing through a portion of waveguide 130. Due to diffraction of light by the grating, each k-vector has a different direction. For example, a first k-vector 210 may correspond to light entering waveguide 130, a second k-vector 220 may correspond to light propagating within waveguide 130 (i.e., guided by TIR), and a third k-vector 230 may correspond to light leaving waveguide 130.

[0027] k-space graph 200 includes several regions defined by a constant radius k. Free space region 240 is a region of k-space graph 200 defined by a free space k value (k...). o The region within a circle of constant radius is defined by the magnitude of k in k-space. In other words, the free space region is defined by a circle with radius 1 centered at the origin of k-space. When the k vector is in the free space region 240, light propagates in free space, such as from the display 110 or to the eye 120.

[0028] The guiding region 250 is outside the free space region 240 of the k-space diagram 200 and is defined by the refractive index (i.e., n) of the waveguide (i.e., substrate) material. sub The region within a constant radius circle defined by the normalized k-value of k. In other words, the guiding region 250 is defined on one side by the free space region 240, and on the other side by a region centered at the origin of k-space with a radius of n. sub (For example, 1.5 for some glasses) a circular boundary. When the k vector is in the guiding region 250, the light is guided by the waveguide. In other words, the light undergoes total internal reflection within the waveguide 130.

[0029] The first k-vector 210 corresponding to the IC grating 140, the second k-vector 220 corresponding to the EPE grating 160, and the third k-vector 230 corresponding to the OC grating 150 illustrate the route of the image from the display to the waveguide output, without having further diffraction caused by secondary gratings formed by variations in one or more of the gratings. Therefore, the image 260 of the display 110 (e.g., formed by the user's eye) can be free of (e.g., zero) defects (e.g., trailing, ghosting, color separation).

[0030] A secondary grating is a grating superimposed on a designed (i.e., ideal) grating (i.e., the primary grating) due to defects generated during the grating generation or replication process. As described, the variations can be changes in the grating's material properties (e.g., refractive index, absorptivity, etc.) and / or structural properties (e.g., size, shape, etc.), affecting the uniformity of the grating on a scale larger than the period of the primary grating. For example, a secondary grating can be a variation of the primary grating over a length more than 100 times larger than the period of the primary grating (i.e., the primary grating period). In other words, the secondary grating period (Λ) s It can be greater than the primary grating period (Λ). p ).

[0031] The light that interacts with the grating can be described by the grating equation (1) shown below.

[0032]

[0033] In the grating equation (1), the normalized k vector It is the k-vector of the beam incident on the grating (i.e., the incident light, the incident beam), and It is the normalized k-vector from the beam diffracted from the grating (i.e., the diffracted light, the diffracted beam). Although not explicitly stated, the incident and diffracted light can be polarized in a plane parallel to the plane formed by the k-vector and the surface normal vector 127 of the grating. In other words, the incident light can be polarized in a plane having the surface normal vector of the substrate.

[0034] In the grating equation (1), λ o It is the wavelength of the incident light (i.e., the incident wavelength). Wavelength (λ) o )and Multiply the k-space vectors. In the term In the diagram, S is the diffraction order of the secondary grating, and Λ S It is the period of the secondary grating, and It is the k-space unit vector (i.e., direction) of the secondary grating. In the term... In this context, P is the diffraction order of the primary grating, and Λ P It is the period of the primary grating, and Let be the k-space unit vector (i.e., direction) of the primary grating. The directions of the primary and secondary gratings can be orthogonal in k-space. The diffraction order (S) of the secondary grating and the diffraction order (P) of the primary grating can be positive and negative integers including zero (e.g., ... -3, -2, -1, 0, +1, +2, +3...), where the zero order (e.g., S = 0) indicates no diffraction due to the grating. For example, S = 0 at a specific wavelength can correspond to the absence of a secondary grating at that specific wavelength (i.e., no long-distance variation).

[0035] The grating equation (1) implies that a single incident beam can produce multi-order diffracted light. For Figure 1 For a waveguide display, it may be desirable for the grating equation to have P = +1 and S = 0, such that only light from the primary grating is in the free space region 240, in order to prevent any secondary series from being included in the image 260 of the display 110. Figure 2 The illustration shows examples of this situation in k-space and image space.

[0036] Figure 3 It is a diagram. Figure 1 The k-space plot shows the effect of variations in the grating of the waveguide display. In k-space plot 300, only the k-vectors associated with the OC grating are illustrated. This plot includes the incident k-vector 310 (i.e., The incident k-vector is diffracted by the OC grating. In this embodiment, the OC grating includes variations that create a secondary grating (i.e., artifacts). Therefore, light is diffracted according to grating equation 1. Although not required, in this embodiment, the secondary grating is orthogonal to the primary grating. Therefore, the k-vector corresponding to the secondary grating can be orthogonal to the k-vector corresponding to the primary grating. The k-vector corresponding to the secondary grating is shorter than the k-vector corresponding to the primary grating because, in this example, the period (Λ) of the secondary grating is shorter. s The period of the primary grating is greater than that of the secondary grating (Λ). p (i.e., Λ) s >Λ p ).

[0037] The series within the free space region 240 of k-space can be coupled to the user's eye 120 (i.e., can be visible). The visible diffraction series correspond to the vector 320 of P = +1, S = 0 (i.e., diffraction from only the primary grating); vector 321 of P = +1, S = +1k; vector 322 of P = +1, S = +2k; vector 323 of P = +1, S = -1k; and vector 324 of P = +1, S = -2k. Figure 3 The P = +1, S = +3k and P = +1, S = -3k vectors shown generate light in the guide region 250, and are therefore retained in the waveguide and invisible to the user's eye. Similarly, other primary grating (i.e., P) orders (0, -1, +2) (not shown) fall outside the free space region and are invisible to the user's eye 120. In other words, the non-propagation region 330 can be a k-space region outside the guide region 250. No grating orders exist in the non-propagation region 330. For example, if the wavelength is much larger than the grating (i.e., the grating is subwavelength), it will not diffract from the grating.

[0038] Figure 4 It corresponds to the possible implementation of this disclosure. Figure 3 The image is a k-space diagram. As shown, image 400 includes a doppelganger corresponding to the secondary grating, spatially offset from the primary image 405 from the primary grating (i.e., P = +1, S = 0). The interval 410 between the doppelgangers may correspond to the period (Λ) of the secondary grating. s For example, as the period of the secondary grating increases, the interval 410 between the superimposed images can decrease, making the primary image 405 from the primary grating appear blurry or fuzzy. This disclosure describes systems and methods for conveniently identifying and characterizing gratings that have one or more secondary gratings in addition to their primary (i.e., designed) gratings.

[0039] According to the grating equation (1), the momentum shift in k-space (i.e., the redirection in real space) is related to the incident wavelength (λ). oThe primary grating period is proportional to the secondary grating period, and as mentioned above, the primary grating period is smaller than the secondary grating period (i.e., Λ). p <Λ s By increasing the incident wavelength to a value greater than that of the substrate (n) sub The test wavelength (λ) is much larger than Λp in ) t In this case, light is no longer affected by the grating (e.g., diffraction). In k-space, this could correspond to having a region larger than the free space region (i.e., 1) and a region larger than the guiding region (i.e., n). sub The magnitude of ) is the k-vector associated with the primary grating. Although λ o Increase to the test wavelength (i.e., λ) t >λ o However, the test wavelength (λ) t It can still be smaller than Λ s This ensures that the k-vector associated with the order of the secondary grating lies in the free space region of the k-space (i.e., <1).

[0040] Figure 5 This is the k-space diagram for testing the grating. In the test, an incident light beam is projected onto the grating in a direction perpendicular to its surface. In k-space, the incident light begins at the center (in the free space region 240). The incident light is at the test wavelength, such that the first diffraction order (P = +1) of the primary grating falls in the non-propagation region. Therefore, the only order present (i.e., visible) from the primary grating is the P = 0 order (i.e., no diffraction from the primary grating). In other words, the primary grating period is subwavelength, such that the test light is not diffracted by the primary grating. However, the secondary grating is not subwavelength, therefore in the free space region of k-space (i.e., ... In the test, the light of the test wavelength is diffracted into two visible orders (i.e., S = +1 and S = -1).

[0041] By analyzing the diffracted light, aspects of the secondary grating can be determined. For example, visible diffracted light can indicate the presence of the secondary grating. Furthermore, the separation of diffraction orders can indicate the period of the secondary grating (see grating equation (1)), and the orientation of the diffraction orders can indicate the orientation of the secondary grating.

[0042] Used to implement Figure 5 The test wavelength (λ) under the conditions shown in the diagram t The first condition corresponds to having a refractive index greater than that of the waveguide (i.e., the grating substrate) (i.e., n). su The normalized magnitude of the k-vector of the primary grating light (S = 0, P = +1). Assume the test light is incident perpendicularly and parallel polarized (i.e., k...). i If S = 0), then the first boundary of the range of test wavelengths can be derived from the grating equation (1) of S = 0, as shown below.

[0043]

[0044] When Figure 4 As shown, when P = +1, equation (2) above simplifies to λ. t >n sub Λ p .

[0045] Used to implement Figure 5 The test wavelength (λ) under the conditions shown in the diagram t The second condition corresponds to the k-vector of the second grating light (S = +1, P = 0) having a normalized value less than one (i.e., in the free space region). Assume the test light is incident perpendicularly and parallel polarized (i.e., k...). i If =0), then the second boundary of the test wavelength range (i.e., the test wavelength range) can be derived from the grating equation (1), as shown below.

[0046]

[0047] When S = +1, this can at least be considered as the order of the detection secondary grating, and equation (2) above simplifies to λ. t <Λ s .

[0048] Therefore, the range of test wavelengths used to measure changes in the grating (i.e., defects) is shown in the following equation.

[0049] n sub Λ p <λ t <Λ s (4)

[0050] Figures 6A to 6C The figure illustrates a grating test system according to a possible embodiment of the present disclosure. The grating test system (i.e., test system 600) may include components configured to generate and project a test wavelength (λ). t The laser 610 is a light source. In some embodiments, the laser 610 may be tunable to determine a specific test wavelength within the aforementioned test range and / or the maximum or minimum wavelength of the test range itself (i.e., n). sub Λ P Λ SLaser 610 can be transmitted to a first optical stage 620 via a transmission medium (e.g., free space, optical fiber). The first optical stage 620 may include one or more optical components (e.g., pinholes, lenses, mechanical positioners) configured to spatially filter, collimate, shape, and / or translate (e.g., x / y translation) the light from laser 610. Test system 600 may also include a second optical stage 630 configured to process the light such that the aforementioned test conditions (e.g., perpendicular incidence, parallel polarization) can be achieved. The second optical stage 630 may include one or more components (e.g., dichroic beam splitters, waveplates) configured to polarize the light from laser 610. Alternatively or additionally, the second optical stage 630 may include components and circuitry (e.g., photodetector circuitry) for monitoring the intensity of laser 610. In possible embodiments, the monitored intensity is fed back to the laser to stabilize the power, which can help counteract polarization fluctuations.

[0051] The test system 600 may also include a grating under test (GUT 647). The GUT 647 may be a grating in waveguide 130, such as... Figure 1 As shown, or simply, a substrate including a primary grating in the primary grating region (of the substrate). In test system 600, GUT 647 can be mounted in a grating positioner 640 configured to control the relative position of GUT 647 such that test region 645 can be illuminated by light from a laser (i.e., fixed to the grating positioner). For example, the test positioner can be configured to move the grating in the X or Y direction, as... Figure 6A As shown in the diagram. The test area can have a relative (e.g., greater than) the secondary grating period (Λ). S The size (e.g., diameter) (e.g., 2Λ) S ≤Test area≤10Λ S In other words, the test area 645 (i.e., the spot size) can be large enough to encompass long-distance variations of the primary grating, which optically behaves as a secondary grating.

[0052] As discussed, the light from the laser is at the test wavelength (λ) that does not interact with the primary grating (e.g., diffraction) but does interact with the secondary grating (e.g., diffraction). t Defects (i.e., artifacts) in a grating (i.e., a primary grating) can be determined by sensing one or more characteristics of diffraction caused by a secondary grating. Therefore, the test system 600 includes devices and components for measuring diffraction at various locations on the grating. By analyzing the diffraction (e.g., diffraction order) of the secondary grating at various locations (i.e., test area, test point, scan position, etc.), the characteristics of long-distance variations in the primary grating can be determined.

[0053] The test system 600 also includes an imaging lens 650 configured to focus light from the GUT 647 onto a camera 660. The imaging lens 650 may be positioned between the GUT and the camera 660 at a distance 670 of approximately (e.g., ±5%) one focal length (f) from the GUT 647, such that the light from the imaging lens is focused at a very large focal length (e.g., infinity). The camera 660 may be an electronic camera (e.g., CCD, CMOS) configured to capture a digital image (i.e., a raster image) of the light from the imaging lens 650.

[0054] Test system 600 may include controller 695. Camera 660 may be communicatively coupled to processor 695 (e.g., wired, wireless, via memory). Processor 695 may be configured by software instructions (e.g., retrieved from a non-transitory computer-readable medium) to determine the position and / or pattern of light from a grating captured as a grating image by camera 660. Processor 695 may also be configured to determine characteristics of GUT 647 based on these positions and / or patterns. In some embodiments, processor 695 may also be configured to control laser 610, camera 660, and / or grating positioner 640 to automate the grating testing process by sequentially acquiring grating images from multiple different test areas as the grating is moved to multiple different test areas. In other embodiments, controller (not shown) may control the acquisition of grating images from various test areas on GUT 647.

[0055] Figure 6A The illustrated test system 600 captures a grating image from a test region 645 in a first position. In the first position, the test region 645 is aligned with a portion of the grating that does not have a secondary grating (i.e., only the primary grating). As previously discussed, the test wavelength (λ) T Light can pass through the primary grating without diffraction. In this case, the imaging lens 650 and the camera 660 can generate a grating image with a single beam.

[0056] Figure 6B The illustrated test system 600 captures a grating image from a test area 645 in a second position. In this second position, the test area 645 is aligned with a portion of the grating that has a secondary grating in addition to the primary grating. As previously discussed, the test wavelength (λ) T Light can pass through a secondary grating with diffraction. In this case, the imaging lens 650 and the camera 660 can generate a grating image with multiple beams separated by a diffraction distance 690 in the image.

[0057] Figure 6CThe illustrated test system 600 captures a grating image from a test region 645 in a third position. In the third position, the test region 645 is aligned with a grating portion that has a secondary grating in addition to the primary grating. The secondary grating can be varied over the length of the GUT 647 because it is uncontrolled (i.e., based on variation). In this case, the secondary grating in the third position has a different secondary wavelength than the secondary grating in the second position (e.g., a shorter secondary wavelength Λ). S As discussed previously, the test wavelength (λ) T Light can pass through a secondary grating with diffraction. In this case, the imaging lens 650 and the camera 660 can generate a grating image with multiple beams (i.e., diffraction orders) separated by a diffraction distance 690 in the image, and the number and spacing of the multiple beams can help determine the secondary wavelength from the test area 645 in the third position.

[0058] Figure 7 It is made by, for example Figure 6C An example of a grating image captured by a grating test system according to an embodiment of the present disclosure is shown. Image 700 includes a primary order 750 corresponding to light not diffracted by GUT 647. The image also includes diffraction orders 750 corresponding to light diffracted by the secondary grating of GUT 647. The image can be processed (e.g., by processor 695) to determine the characteristics of the primary order 750, diffraction orders 730, and / or the pattern formed by the primary order and diffraction orders. For example, measurements (e.g., centroids) of each of the diffraction orders 730 can determine the pixel position of each diffraction order in the image. Pixel positions can be compared (e.g., subtracted) to determine the diffraction distance 690 between primary orders and diffraction orders or between diffraction orders. In the above arrangement where the imaging lens and the GUT are separated by a focal length (f), the diffraction distance (d) can be related to the angle (θ) of the diffraction order (e.g., sinθ = d / f) (i.e., the diffraction angle 68°), and the angle of the diffraction order can be related to the wavelength (Λ) of the secondary grating. S This information is relevant. In some cases, it can be used to determine variations in the primary grating period or feature size that lead to the generation of the secondary grating. Various other measurements can be made based on the diffraction pattern. For example, the primary order position and / or order angle 720 can be correlated with the position and / or angle of the secondary grating in the test area.

[0059] Analysis of raster images can occur after each raster image is acquired. For example, when only secondary raster detection is required, it may not be necessary to associate each raster image with a location (i.e., location information). Instead, each raster image can be evaluated as good (e.g., no secondary raster) or bad (secondary raster). Furthermore, in some cases, the raster testing process can be terminated whenever a secondary raster is detected.

[0060] Image analysis can occur after all raster images have been acquired. For example, each raster image can be associated with a position on the raster based on position information 751 derived from raster locator 640. In some cases, mechanical step size (i.e., step length) and scan type (e.g., raster scan) can provide position information 751 that can be used to determine the relative position of each raster image. The step size can be selected based on a balance between the resolution and speed of the test. For example, when high-resolution testing is required, the step size can be smaller than the diameter of the test area 645. Alternatively, when high-speed testing is required, the step size can be larger than the diameter of the test area 645. The captured images and their corresponding position information 751 can be stored together in a database coupled to a memory (not shown) of processor 695.

[0061] A spatial map of the secondary grating (e.g., a spatial map of the secondary grating period) can be created based on a pattern (e.g., a grid) corresponding to the test area of ​​the grating test. This map can be used to map the extent of one or more secondary gratings. The map can also be used to determine how the secondary grating changes (i.e., varies) with location, which can help determine long-distance variations in the primary grating period and / or the primary grating feature size responsible for the secondary grating.

[0062] While some examples of raster image measurements have been presented, they may not represent an exhaustive list of possible raster image measurements and are therefore not intended to limit or exclude other obvious variations.

[0063] Figure 8 This is a flowchart of a method for testing a grating according to an embodiment of this disclosure. Method 800 includes tuning a laser 810 to a test wavelength. The test wavelength is a wavelength within the test wavelength range. In some cases, tuning 810 includes determining the test wavelength.

[0064] Determining the test wavelength may involve projecting light of a first wavelength from a laser onto a grating such that the diffraction order of the primary grating exists (i.e., it is visible). The laser wavelength is then tuned (e.g., increased) to a test wavelength at or below the wavelength where the diffraction order of the primary grating does not exist (i.e., the primary grating no longer interacts with the light). This can be determined experimentally or through prior knowledge of the period of the primary grating.

[0065] Method 800 also includes guiding a laser beam from a laser 820 onto a test area on the grating under test and capturing an image (i.e., a grating image) of the light collected (e.g., focused) from the test area 830. Method 800 further includes analyzing the collected image to determine information about the grating (i.e., characteristics of the secondary grating). The test area of ​​the grating 850 can then be moved by repositioning the grating, repositioning the laser, or both, and the test process can be repeated for multiple different test areas.

[0066] In one example, analysis 840 (i.e., analysis) can determine the presence or absence of a secondary grating (i.e., secondary grating detection 842) by the presence or absence of a diffraction order at a certain location in the test area in the grating image.

[0067] In another example, the analysis can identify the location of the secondary grating within a substrate of a waveguide, such as that used in a waveguide display (i.e., secondary grating location 844). For example, the secondary grating may be located at a specific location when determining the diffraction order of a test wavelength. In some embodiments, this positioning process can be used to map the boundaries of the region including the secondary grating.

[0068] In another example, the number of 846 secondary gratings can be determined. For example, in some embodiments, multiple secondary gratings may be located on the area occupied by the gratings (e.g., on a region of the substrate). The multiple secondary gratings may have the same grating wavelength or different grating wavelengths and may be located in different regions separated by a region containing only primary gratings. After testing, the number of secondary gratings can be determined as the number of different regions with secondary gratings identified during the automatic scanning of the gratings.

[0069] In another example, some characteristics of the 848-secondary grating can be determined. For example, the period of the secondary grating can be determined based on the diffraction order spacing in the grating image. In possible implementations, the period of the secondary grating can be used to determine the variation of the primary grating period, the primary grating fill factor, and / or the primary grating feature size at distances greater than the primary grating period.

[0070] The method for testing gratings can be used to test gratings or systems as part of a production process. For example, gratings for waveguides used in waveguide display systems can be tested because grating images can be collected from grating testing as quickly as the grating can be mechanically scanned. Analysis of the grating images can occur during or after the mechanical scan. When analysis is performed after the mechanical scan, the grating images acquired during the scan can be stored in memory along with associated position information 751. This disclosed grating testing method can reduce the cost and time required for testing gratings and provides a means to understand changes occurring on a physically large scale compared to the period of the primary grating.

[0071] Publicly available grating tests can generate information that can be used to facilitate other grating tests. For example, locations identified as having secondary gratings can be identified for testing using different modalities, such as microscopy. Microscopic testing (e.g., SEM, AFM, TEM) can be used to determine grating defects in more detail. For example, subsequent microscopic testing can quantify changes in the primary grating period, primary grating fill factor, and / or primary grating feature size that cause secondary gratings (i.e., image artifacts). This approach can advantageously save time compared to scanning the entire grating with a microscope, as the slower microscope only scans the areas with detected secondary gratings.

[0072] Typical embodiments have been disclosed in the specification and / or drawings. This disclosure is not limited to such exemplary embodiments. The use of the term "and / or" includes any one or more of the associated listed items and all combinations thereof. These figures are schematic and therefore not necessarily drawn to scale. Unless otherwise indicated, particular terms are used in a general and descriptive sense and not for limiting purposes.

[0073] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Methods and materials similar to or equivalent to those described and used herein may be used in practice or testing within this disclosure. As used in the specification and appended claims, the singular forms “a,” “an,” and “the” include multiple referents unless the context clearly indicates otherwise. As used herein, the term “comprising” and variations thereof are used synonymously with the term “including” and variations thereof and are open-ended, non-limiting terms. The terms “optionally” or “optionally” as used herein mean that a feature, event, or condition subsequently described may or may not occur, and the description includes instances of the occurrence and non-occurrence of said feature, event, or condition. A range herein may be expressed as from “about” one particular value and / or to “about” another particular value. When such a range is expressed, an aspect includes from one particular value and / or to another particular value. Similarly, when values ​​are expressed as approximate values, the use of the antecedent “about” will help to understand that the particular value forms another aspect. It should be further understood that the endpoints of each range are important both in relation to and independent of the other endpoint.

[0074] Some implementations can be implemented using various semiconductor processing and / or packaging technologies. Some implementations can be implemented using various types of semiconductor processing technologies associated with semiconductor substrates, including but not limited to silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), etc. Additionally, some implementations can use single-crystal diamond, HOYATMTAFD55-W, or other display waveguide glass types. Furthermore, some implementations can use optical-grade plastics.

[0075] While certain features of the described embodiments have been described as such herein, many modifications, substitutions, alterations, and equivalents will now occur to those skilled in the art. Therefore, it should be understood that the appended claims are intended to cover all such modifications and alterations falling within the scope of the embodiments. It should be understood that they are presented by way of example only and not limitation, and various changes in form and detail may be made. Any part of the apparatus and / or method described herein can be combined in any combination, except for mutually exclusive combinations. The embodiments described herein may include various combinations and / or sub-combinations of the functions, components, and / or features of the different embodiments described.

[0076] It will be understood that in the foregoing description, when an element is referred to as being on, connected to, electrically connected to, coupled to, or electrically coupled to another element, the element may be directly on, connected to, or coupled to the other element, or one or more intermediary elements may be present. Conversely, when an element is referred to as being directly on, directly connected to, or directly coupled to another element, no intermediary element is present. Although the terms “directly on,” “directly connected to,” or “directly coupled to” may not be used throughout the detailed description, elements shown as being directly on, directly connected to, or directly coupled may be referred to as such. The claims of this application (if any) may be modified to record exemplary relationships described in the specification or shown in the drawings.

[0077] As used herein, the singular form may include the plural form unless the context clearly indicates otherwise. Spatial relative terms (e.g., above, above, upper, below, under, lower, etc.) are intended to cover different orientations of the equipment in use or operation other than those depicted in the figures. In some embodiments, the relative terms "above" and "below" may include vertically above and vertically below, respectively. In some embodiments, the term "adjacent" may include "laterally adjacent" or "horizontally adjacent".

Claims

1. A method for testing a grating, comprising: Light from a laser tuned to the test wavelength is directed to a first test area on the grating; A raster image is captured based on the light passing through the first test area; The grating image is analyzed to measure diffraction from a secondary grating, and when the measured diffraction is non-zero, the characteristics of the secondary grating are determined from the diffraction. The secondary grating is generated by a defect in the primary grating, which has a primary grating period that is a subwavelength of the test wavelength such that the test wavelength is not diffracted. as well as The steps of guiding, capturing, and analyzing are repeated at a second test area on the grating to characterize the defects of the primary grating.

2. The method according to claim 1, wherein, The defect of the primary grating is that the characteristics of the primary grating vary spatially over a distance that is more than 100 times larger than the period of the primary grating.

3. The method according to claim 2, wherein, The characteristics are the primary grating period, primary grating fill factor, primary grating feature size, primary grating feature shape, or primary grating refractive index.

4. The method according to claim 1, wherein, The secondary grating has a secondary grating period that is not a subwavelength of the test wavelength, such that the test wavelength λ t Within the range given by the following formula: ,in: n sub It is the refractive index of the grating. P It is the primary grating period, and S It is the secondary grating period.

5. The method according to claim 1, wherein, Guiding the light from the laser to the first test area on the grating includes: The light from the laser is projected such that it travels in a direction aligned with the surface normal vector of the grating; and The light is polarized such that the light and the surface normal vector of the grating are in the same plane.

6. The method according to claim 1, wherein, Analyzing the grating image to measure diffraction from the secondary grating and determining the characteristics of the secondary grating from the diffraction includes: When the measured diffraction is non-zero, the position information is associated with the grating image; and The position of the secondary grating is identified based on the location information.

7. The method according to claim 6, further comprising: A microscope is used to scan the position of the secondary grating to measure the changes in grating period, grating feature size, or grating fill factor relative to the corresponding design values.

8. The method according to claim 1, wherein, Analyzing the grating image to measure diffraction from the secondary grating and determining the characteristics of the secondary grating from the diffraction includes: Determine the diffraction distance between the diffraction order and the primary order in the grating image; and The secondary grating period of the grating image is determined based on the diffraction distance.

9. The method according to claim 8, further comprising: Determine the orientation between the diffraction order and the primary order; as well as The orientation of the secondary grating is determined based on the orientation.

10. A system for testing gratings, comprising: A substrate, the substrate including a primary grating in a primary grating region; A laser configured to project light of a test wavelength onto a test area within the primary grating region, the test wavelength being non-diffracted by the primary grating; A camera configured to capture a grating image of the light after it passes through the test area; as well as Processor, the processor being configured by software instructions to: The diffraction order in the grating image is detected, the diffraction order corresponding to diffraction from a secondary grating having a secondary grating period greater than that of the primary grating; as well as The diffraction order is analyzed to determine the characteristics of the secondary grating.

11. The system according to claim 10, wherein, The secondary grating corresponds to the variation of the primary grating characteristics over a distance at least 100 times larger than the period of the primary grating.

12. The system according to claim 11, wherein, The characteristics are the primary grating period, primary grating fill factor, primary grating feature size, primary grating feature shape, or primary grating refractive index.

13. The system according to claim 10, wherein, The processor is further configured to: Control the grating positioner coupled to the substrate to move the test area to multiple different test areas in the primary grating region; as well as The steps of analyzing the diffraction order detected in the grating image from each of the plurality of different test regions are repeated to determine the characteristics of the secondary grating.

14. The system of claim 10, further comprising: An optical turntable configured to guide light in a direction aligned with the surface normal vector of the substrate; as well as A polarizer configured to polarize the light from the laser such that the light is in the same plane as the surface normal vector of the substrate.

15. The system according to claim 10, wherein: The test wavelength (λ) t It is within the test wavelength range given by the following formula: ,in: n sub It is the refractive index of the grating. P It is the primary grating period of the primary grating, and S It is the secondary grating period of the secondary grating.

16. The system of claim 10, further comprising: An imaging lens with a focal length is positioned between the grating and the camera, approximately one focal length away from the grating.

17. The system according to claim 10, wherein, The substrate is the waveguide of the waveguide display system.

18. A method for testing a waveguide display, comprising: Light from a laser is sequentially guided to multiple different test regions on the primary grating of the waveguide display, the light being at a test wavelength larger than the period of the primary grating, so that the light is not diffracted by the primary grating. A raster image of the light is captured sequentially after the light passes through each of the plurality of different test areas; Detect the diffraction order within one or more of the plurality of grating images, wherein the diffraction order corresponds to a secondary grating; as well as The diffraction order is analyzed to determine the characteristics of the secondary grating in each test region corresponding to each of the one or more grating images that include the diffraction order.

19. The method of claim 18, further comprising: Determine the positional information corresponding to the one or more grating images, including diffraction orders; as well as The spatial map of the secondary grating is generated based on the location information.

20. The method of claim 19, further comprising: The changes in the secondary grating are determined based on the spatial diagram.

Images