Asymmetric metrology tool for reflective waveguide

Abstract

Embodiments described herein provide an asymmetric optical metrology system for evaluating and checking the performance of an optical element, such as an augmented reality (AR) waveguide combiner. The system utilizes an asymmetric optical configuration and compound eye illumination to enhance the detection limit of image definition and the accuracy of brightness uniformity. By employing different lenses with various focal lengths, the system improves the sampling rate in the angular space, solving the challenges of shape factor limits and pixel density inherent in known metrology tools. Embodiments described herein provide improved contrast and clear image details, as well as a compact design that is suitable for the development, optimization, and quality control of optical elements, such as AR waveguide combiners.

Description

Technical Field

[0001] The embodiments of this disclosure generally relate to the field of optical metrology. More specifically, the embodiments described herein provide a metrology system and a method for measuring optical elements. Background Technology

[0002] Virtual reality is generally considered to be a computer-generated simulated environment in which the user has an apparent physical presence. Virtual reality experiences can be generated in 3D and viewed using head-mounted displays (HMDs), such as glasses or other wearable display devices, which have near-eye display panels as lenses to display a virtual reality environment that substitutes for the real environment.

[0003] However, augmented reality enables experiences where users can still see their surroundings through the display lenses of glasses or other HMD devices, and also see images of virtual objects generated to be displayed and appear as part of the environment. Augmented reality can include any type of input, such as audio and haptic input, as well as virtual images, graphics, and videos of the environment that enhance or augment the user experience. As an emerging technology, augmented reality faces many challenges and design constraints.

[0004] One such challenge is measuring image quality standards for optical components. Conventional optical metrology tools often utilize symmetrical optical configurations, where the same lens system is used for both projection and detection. This design can lead to limitations in shape factor and pixel density, which can negatively impact the tool's ability to accurately measure certain performance metrics. Therefore, there is a need in the art for a metrology system and a method for measuring optical components.

[0005] Therefore, there is a need for improved optical metrology tools and methods that can overcome these limitations and provide more accurate and reliable measurements of the performance and quality of optical components, including reflective waveguides used in AR, VR, and other advanced display technologies. Summary of the Invention

[0006] In one embodiment, an optical metrology system is provided. The optical metrology system includes an optical engine configured to be aligned with an input coupler of an optical element. The optical engine includes a projection lens having a first focal length, arranged to receive a test pattern and couple the test pattern to the input coupler. A reflection detector is configured to be aligned with an output coupler of the optical element, the reflection detector including a camera lens having a second focal length, the camera lens being arranged to receive a reflection test pattern from the output coupler and project the reflection test pattern onto a camera of the reflection detector.

[0007] In another embodiment, an optical metrology method is provided. The method includes: aligning an optical engine with an input coupler of an optical element, the optical engine including a caliper and a projection lens having a first focal length; projecting a test pattern onto the optical element using the optical engine; aligning a reflection detector with an output coupler of the optical element, the reflection detector including a camera lens having a second focal length; receiving a reflection test pattern from the optical element using the reflection detector; and analyzing the reflection test pattern to extract metrological measurements of the optical element. Attached Figure Description

[0008] To gain a more detailed understanding of the features described above, a more specific description of the present disclosure, which has been briefly summarized above, can be obtained by referring to embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings illustrate only exemplary embodiments and should not be construed as limiting their scope, and other equally effective embodiments may be permitted.

[0009] Figure 1A This is a perspective front view of the substrate according to the embodiments described herein.

[0010] Figure 1B This is a perspective front view of an optical element according to the embodiments described herein.

[0011] Figure 2 This is a schematic diagram of an optical metrology system according to the embodiments described herein.

[0012] Figure 3 This is a schematic diagram of the optical engine and reflection detector of an optical metrology system according to the embodiments described herein.

[0013] Figure 4 This is a flowchart of an optical metrology method according to the embodiments described herein.

[0014] To facilitate understanding, the same reference numerals are used to denote common elements in the figures where possible. Elements and features of one embodiment are contemplated to be advantageously incorporated into other embodiments without further description. Detailed Implementation

[0015] Figure 1A This is a perspective front view of a substrate 100 according to an embodiment described herein. The substrate includes a plurality of optical elements 102 disposed on a surface 101 of the substrate 100. The optical elements 102 are waveguide combiners for virtual reality, augmented reality, or mixed reality.

[0016] The substrate 100 can be any substrate used in the art, and depending on the application of the substrate 100, it can be opaque or translucent for a selected laser wavelength. Furthermore, the substrate 100 can have different shapes, thicknesses, and diameters. For example, the substrate 100 can have a diameter of about 150 mm to about 300 mm. The substrate 100 can have a circular, rectangular, or square shape. The thickness of the substrate 100 can be between about 300 μm and about 1 mm. Although only nine optical elements 102 are shown on the substrate 100, any number of optical elements 102 can be disposed on the surface 101.

[0017] Figure 1B This is a perspective front view of optical element 102. It should be understood that the optical element 102 described herein is an exemplary optical element, and other optical elements may be used in or modified to implement aspects of this disclosure. Optical element 102 includes a plurality of optical element structures 103 disposed on a surface 101 of substrate 100. Optical element structures 103 may be nanostructures with submicron dimensions. Each region of optical element structure 103 corresponds to one or more gratings, such as a first grating 104a, a second grating 104b, and a third grating 104c.

[0018] In some embodiments that can be combined with other embodiments described herein, optical element 102 includes at least a first grating 104a corresponding to an input coupling grating and a third grating 104c corresponding to an output coupling grating. In some embodiments that can be combined with other embodiments described herein, optical element 102 also includes a second grating 104b corresponding to an intermediate grating. In some embodiments, the input coupling grating and the output coupling grating are also referred to as an input coupler and an output coupler. Optical element structure 103 may be tilted, blazed, binary, or stepped. Optical element structure 103 may have other shapes, including but not limited to circular, triangular, elliptical, regular polygonal, irregular polygonal, and / or irregularly shaped cross-sections.

[0019] In operation, the first grating 104a receives an incident beam (virtual image) of a certain intensity from a light source. The incident beam is split by optical element structure 103 into beams having all the intensities of the incident beam to guide the virtual image to a second grating (if used) 104b or a third grating 104c. In some embodiments that can be combined with other embodiments described herein, the beam undergoes total internal reflection (TIR) ​​through optical element 102 until it contacts the optical element structure 103 of the second grating 104b. The optical element structure 103 of the second grating 104b diffracts the beam into a diffracted beam, which undergoes TIR through optical element 102 to reach the optical element structure 103 of the third grating 104c. The optical element structure 103 of the third grating 104c couples the diffracted beam output to the user's eye to modulate the field of view of the virtual image generated by the light source from the user's perspective and further increase the user's viewing angle of the virtual image. In other embodiments that can be combined with other embodiments described herein, the beam undergoes TIR through optical element 102 until the beam contacts optical element structure 103 of third grating 104c and outputs coupling to modulate the field of view of the virtual image generated by the light source.

[0020] To ensure that optical element 102 meets image quality standards, metrological measurements of the manufactured optical element 102 can be obtained. The metrological measurements of each optical element 102 are tested to ensure that predetermined values ​​are met. Embodiments of the optical metrology system 200 described herein provide the ability to obtain multiple metrological measurements at increased production volumes. These metrological measurements include one or more of the following: angular uniformity measurement, contrast measurement, efficiency measurement, color uniformity measurement, modulation transfer function (MTF) measurement, field of view (FOV) measurement, ghosting measurement, and eye-friendly zone measurement.

[0021] Figure 2 This is a schematic cross-sectional view of an optical metrology system 200 according to an embodiment described herein. The optical metrology system 200 includes a body 201 having a first opening 203 and a second opening 205 to allow a stage 207 to move through the first opening and the second opening. The stage 207 is operable to move within the body 201 of the optical metrology system 200 in the X, Y, and Z directions. The stage 207 includes a tray 209 operable to hold an optical element 102 (as shown herein) or one or more substrates 100.

[0022] The optical metrology system 200 is operable to obtain one or more metrological measures, including one or more of angular uniformity, contrast ratio, efficiency, color uniformity, MTF, FOV, ghosting, or eye-friendly zone measures. The stage 207 and tray 209 may be transparent, such that the metrological measures obtained by the optical metrology system 200 are not affected by the translucency of the stage 207 or tray 209. The optical metrology system 200 is communicatively coupled to a controller 220. The controller 220 can be used to facilitate the operation of the optical metrology system 200.

[0023] Controller 220 is coupled to optical metrology system 200. Controller 220 includes a processor 252, memory 254, and support circuitry 256 coupled to each other. Controller 220 is electrically coupled to optical metrology system 200 via wire 258. Processor 252 can be any form of general-purpose microprocessor or general-purpose central processing unit (CPU), each of which can be used in industrial environments such as programmable logic controllers (PLCs), supervisory control and data acquisition (SCADA) systems, general-purpose graphics processing units (GPUs), or other suitable industrial controllers. Memory 254 is non-transitory and can be readily available memory, such as random access memory (RAM), read-only memory (ROM), or one or more of any other form of local or remote digital storage device. Memory 254 contains instructions that, when executed by processor 252, facilitate the execution of method 400. The instructions in memory 254 are in the form of a program product, such as a program that implements the methods of this disclosure. The program code of the program product may conform to any of a variety of different programming languages. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer, such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips, or any type of solid-state non-volatile semiconductor memory), on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks or hard disk drives in a disk drive or any type of solid-state random access semiconductor memory), on which variable information is stored. Such computer-readable storage media, when carrying computer-readable instructions that direct the function of the methods described herein, are examples of this disclosure.

[0024] The optical metrology system 200 includes an upper portion 204 oriented toward the top side of the optical element 102 and a lower portion 206 oriented toward the bottom side of the optical element 102. The upper portion 204 of the optical metrology system 200 includes an alignment camera 208, a light engine 210, and a reflection detector 212. The alignment camera 208 is operable to determine the position of a stage 207. The alignment camera 208 is also operable to determine the position of a substrate 100 disposed on the stage 207. The light engine 210 is operable to project light. In some embodiments that can be combined with other embodiments described herein, the light engine 210 projects a test pattern onto a first grating 104a of the optical element 102. The reflection detector 212 detects a beam of light output coupled from a third grating 104c of the optical element 102. The output coupled beam can be emitted from either the top side 222 or the bottom side 224 of the optical element 102. The output coupled beam may correspond to a test pattern from the light engine 210. The reflectance detector 212 detects one or more images of the test pattern. The controller 220 can be used to process one or more images of the test pattern to extract each measurement.

[0025] The lower portion 206 of the optical metrology system 200 includes a code reader 214 and a transmission detector 216. The code reader 214 and the transmission detector are located on the opposite side of the stage 207, opposite the alignment camera 208, the light engine 210, and the reflection detector 212. The code reader 214 is operable to read codes of the optical element 102, such as quick response (QR) codes or barcodes of the optical element 102. The codes read by the code reader 214 may include identification information and / or instructions for obtaining one or more metrological measurements of the optical element 102. The transmission detector 216 detects a coupled light beam output from the third grating 104c through the bottom side 224 of the substrate 100. In some embodiments that can be combined with other embodiments described herein, the transmission detector 216 is coupled to a transmission detector stage 226. The transmission detector stage 226 is operable to move the transmission detector 216 in the X, Y, and Z directions. The transmission detector stage 226 is operable to adjust the position of the transmission detector 216 to enhance the detection of the output coupled beam projected from the third grating 104c.

[0026] In operation, metrological measurements are obtained by illuminating the first grating 104a of the optical element 102 with the light engine 210. The light engine 210 projects a test pattern onto one or more optical elements 102. The input coupled light undergoes a TIR (transmit-reflection) until the light is output coupled from the optical element 102 (e.g., reflected or transmitted). The reflection detector 212 captures the test pattern as one or more images. These one or more images may correspond to the red, green, and blue channels. These one or more images may also correspond to one or more different metrological measurements. These one or more images are full-field images.

[0027] Figure 3 This is a schematic diagram of the optical engine and reflection detector of an optical metrology system according to the embodiments described herein. The reflection detection module 300 includes an optical engine 210 and a reflection detector 212.

[0028] The light engine 210 includes several optical components designed to work together to generate a high-quality, uniform light beam for testing purposes. These components include a light source 302, such as an LED, that emits light. The light is directed through a first focusing lens 304, and then through a second focusing lens 310. These lenses help collimate the beam, ensuring it remains focused as it travels through the system. Furthermore, the light engine 210 features a first microlens array 306 and a second microlens array 308, which are used to improve the spatial uniformity of the beam by redistributing its intensity across the cross-section of the beam. Finally, the light engine 210 incorporates a test pattern 312 that modulates the beam according to a specific metrological metric. In some embodiments, the test pattern 312 may be generated by a caliper or a microdisplay. The patterned light is then passed through a projection lens 314, which focuses the light onto the optical element under test, such as an AR waveguide combiner. The projection lens has a focal length of approximately 10 mm to approximately 20 mm. For example, the projection lens may include a focal length of approximately 16 mm.

[0029] In the light engine 210, illumination is provided by a light source 302 (such as an LED). Depending on the situation, light from the light source 302 is transmitted through a first focusing lens 304. The focal length of this first focusing lens 304 ranges from 10 mm to 60 mm. A second focusing lens 310 also has a focal length range of 10 mm to 60 mm. This lens is responsible for collimating the light beam originating from the light source 302. A well-collimated beam provides accurate test pattern projection and ensures that the light is parallel and focused. In some embodiments that can be combined with other embodiments described herein, the first focusing lens 304 may be removed. Removing this lens may result in a more compact system.

[0030] To further enhance spatial uniformity and correct the incident angle, the beam is subsequently modulated through a series of microlens arrays, including at least a first microlens array 306 and a second microlens array 308. In operation, light from a first focusing lens 304 is directed into the first microlens array 306, where each individual microlens splits the incident light into multiple smaller beams. This process effectively redistributes light intensity across the beam's cross-section, resulting in improved spatial uniformity. The beam then proceeds to the second microlens array 308. This array is positioned such that it receives light from the first microlens array 306 at an angle. The second microlens array 308 is designed to redirect these angled beams, adjusting their propagation direction to be more parallel to the system's optical axis. This action corrects the beam's incident angle, ensuring that the beam is optically aligned to interact with subsequent optical components and the element under test.

[0031] In some embodiments, the pitch of the first microlens array 306 and / or 308 ranges from 100 μm to 2 mm, and the effective focal length (EFL) ranges from 0.2 mm to 2 mm. In this embodiment, the first and second microlens arrays are identical, and the gap between the first and second microlens arrays should be equal to the focal length of the microlens. In this case, the gap between the first microlens array 306 and the second microlens array 308 is approximately 0.6 mm.

[0032] After passing through the second microlens array 308, the light diverges and is recollided by the second focusing lens 310. The second focusing lens 310 produces a collimated beam that is guided toward the test pattern 312.

[0033] Test pattern 312 serves as a reference image for evaluating the performance of the AR waveguide combiner. Test pattern 312 can be implemented as a caliper patch or a microdisplay, depending on the required resolution and application requirements.

[0034] In some implementations, the grading patch is a high-resolution patterned mask formed using electron beam, ion beam, or photolithography techniques. This method enables nanoscale patterning, allowing for highly precise evaluation of optical components. Depending on the specific evaluation requirements, the grading patch pattern may include a checkerboard pattern, line pair pattern, dot matrix pattern, or a combination of different patterns.

[0035] In other embodiments, a microdisplay can be used as test pattern 312. Microdisplays, such as liquid crystal on silicon (LCOS) modules, digital light processing (DLP) modules, microLEDs, or organic light-emitting diode (OLED) displays, offer flexibility in pattern generation and dynamic adjustment. However, microdisplays typically have a lower resolution limit than calibrated sheets because they are constrained by the pixel size of the display technology.

[0036] The test pattern 312 is then projected onto the AR waveguide combiner using the projection lens 314. The test pattern acts as an object plane and is positioned at the focal length of the projection lens, thereby producing a collimated beam output.

[0037] The projection lens 314 projects the test pattern from the caliper or microdisplay onto the first grating 104a of the optical element 102 (such as an AR waveguide combiner). By placing the test pattern at the focal length of the projection lens, a collimated beam output is created, ensuring high-quality projection onto the waveguide combiner. The projection lens also ensures accurate transmission of the test pattern onto the optical element, enabling reliable evaluation of its performance.

[0038] The distance between the test pattern 312 and the projection lens 314 depends on the working distance. The working distance may differ from the focal length because the mechanical distance may vary due to factors such as lens thickness. However, the test pattern should be effectively positioned at the focal plane of the projection lens, which in this case ranges from 10 mm to 100 mm.

[0039] The reflection detector 212 captures the light reflected from the optical element 102 to evaluate its performance based on the test pattern projected by the light engine 210.

[0040] The reflection detector 212 includes a camera lens 322 and a camera 324. The camera lens 322 is designed to have a large field of view (FOV) to capture the entire test pattern reflected from the AR waveguide combiner. This high-resolution lens ensures that the captured image has sufficient detail to accurately evaluate the image quality and brightness uniformity of the combiner.

[0041] Camera 324 is typically a high-resolution camera equipped with a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensor. These sensors are known for their ability to capture images with high fidelity and high sensitivity. The camera's resolution and pixel size ultimately determine the metrology system's ability to evaluate waveguide combiners at the required level of accuracy.

[0042] In operation, after the light engine 210 projects the test pattern onto the reflection detector 212, the reflection detector captures the light reflected by the third grating 104c of the optical element 102. The camera lens 322 focuses the reflected light onto the camera 324, and the camera 324 captures an image for further analysis. The focal length of the camera lens 322 is approximately 20 mm to approximately 40 mm. For example, the camera lens 322 includes a focal length of 30 mm. By analyzing the captured image, the metrology system can assess the image quality, sharpness, and brightness uniformity of the AR waveguide combiner, thereby allowing for optimization and improvement of its performance.

[0043] The disclosed implementation of the reflection detection module 300 enhances the accuracy of image sharpness detection limits and brightness uniformity through its asymmetrical design and the use of compound eye illumination. The asymmetrical design involves using different lenses with different focal lengths for the projection lens 314 and the camera lens 322. This configuration allows for higher resolution and better sampling in angular space.

[0044] The focal length of the projection lens 314 is smaller than that of the camera lens 322, which allows the high resolution provided by the scribe line (or microdisplay) in the test pattern 312 to be utilized. Since the scribe line can achieve resolution in the sub-micron range, the projection lens can utilize this high resolution to create a sharper test pattern. This sharper test pattern is then projected onto the optical element 102, allowing for a more accurate evaluation of its image quality.

[0045] The camera lens 322 has a longer focal length, which allows it to capture more detail in the projected test pattern reflected from the optical element 102. Using a higher sampling rate, the camera can detect finer details and measure higher frequencies, resulting in a more accurate assessment of the AR waveguide combiner's performance.

[0046] The compound eye illumination in the light engine 210 ensures a high degree of brightness uniformity. This is achieved through the use of a first microlens array 306 and a second microlens array 308. The first microlens array 306 focuses the light onto the second microlens array 308, correcting for any abnormal angles of incidence. This process ensures that all rays illuminate the same point, thus providing a uniform light distribution across the entire test pattern. The second focusing lens 310 then collimates the light before it interacts with the test pattern 312. This uniform light distribution contributes to enhancing the accuracy of brightness uniformity measurements in the optical element 102.

[0047] In operation, the implementation of asymmetric metrology tools is designed to correct lateral distortion, enable high-frequency sampling, mitigate shape factor limitations, and improve resolution.

[0048] Lateral distortion occurs when an image is not uniformly magnified across its entire field of view. In an asymmetric optical system, using different lenses with different focal lengths for the projection lens 314 and the camera lens 322 helps to correct part of this distortion. By having a higher magnification on the camera side, any lateral distortion present in the projected test pattern will be reduced when the camera captures the reflected image from the optical element 102.

[0049] High-frequency sampling is achieved by using a longer focal length for the camera lens 322. This results in greater image magnification, allowing the camera to capture more detail and measure higher spatial frequencies. Consequently, metrological tools can detect finer details in the performance of the AR waveguide combiner, providing a more accurate assessment.

[0050] The use of high-resolution scribe lines (or microdisplays) in the test pattern 312 allows the metrology tool to achieve high resolution. Specifically, the scribe line can achieve resolution down to the sub-micron level, enabling the projection lens 314 to utilize this high resolution to create a sharper test pattern. On the camera side, the longer focal length of the camera lens 322 allows the camera to capture more detail in the projected test pattern, further improving the resolution of the metrology system.

[0051] The shape factor limitation is addressed by using an asymmetric optical configuration, where the focal length of the projection lens 314 is smaller than that of the camera lens 322. This allows for a smaller lens diameter, enabling the projector optics and camera lens to be placed on the same side of the optical element 102. This compact configuration is particularly advantageous for AR glasses applications, where both the light engine and camera module are placed on the same side of the element.

[0052] Figure 4 This is a flowchart of an optical metrology method according to the embodiments described herein. For ease of explanation, reference will be made to... Figure 2 and Figure 3 Method 400 is described using the optical metrology system 200 and the reflection detection module 300 shown herein. Method 400 is operable to be performed in other metrology systems not described herein.

[0053] First, the optical element is correctly positioned and aligned on the stage 207 of the optical metrology system 200. This step lays the foundation for subsequent steps in the metrology process. This positioning ensures that the optical element is correctly aligned with both the optical engine 210 and the reflection detector 212 of the reflection detection module 300.

[0054] The optical element can be an AR waveguide combiner or another type of optical element, typically held in place on a mechanical stage or support that allows for fine-tuning of position and orientation. This ensures that the test pattern projected from the optical engine is accurately coupled to the inner input coupler of the optical element, and that the output coupled light leaving the output coupler is accurately captured by the reflection detector. The optical engine 210 and the reflection detector 212 are aligned relative to the waveguide.

[0055] At operation 402, the light engine 210 uses the light source 302 to generate a light beam and direct the light toward the optical components of the system. The light source 302 can be any suitable type of light source, such as a light-emitting diode (LED), laser, or lamp. The light source 302 is typically controlled by a controller (in...) Figure 3 (Not shown) The controller can adjust parameters such as light intensity and light pulse timing. This allows the metrology tool to adapt to different types of optical elements and test conditions. In some embodiments that can be combined with other embodiments described herein, the light engine 210 is operable to be positioned on a rotary table such that the light engine 210 can be rotated and / or tilted as needed during method 400.

[0056] At operation 404, the light beam is collimated by passing it through a first focusing lens 304 within the light engine 210. Collimation is a technique used in optical systems to ensure that light rays travel parallel to each other. This step is crucial for maintaining the uniformity of the light beam and, therefore, the accuracy of the test pattern projected onto the optical elements. The first focusing lens 304, with a focal length of approximately 30 mm, receives the diverging light beam from the light source 302 and converges it to a point located on its focal plane. This action converts the diverging beam into a collimated beam, in which the light rays move parallel to each other and parallel to the optical axis.

[0057] In some cases, the design of the metrology tool can exclude the first focusing lens 304, thereby allowing the light beam to interact directly with the first microlens array 306 and the second microlens array 308.

[0058] At operation 406, the process involves improving the spatial uniformity of the beam. This step requires guiding the collimated beam onto the first microlens array 306. This microlens array, also known as a compound eye lens, can include a large number of tiny lenses arranged in a uniform array. Each microlens in the array individually focuses the light incident on it, thereby creating multiple distinct 'sub-beams' or 'small beams'.

[0059] The first microlens array 306 has a pitch ranging from 100 μm to 2 mm and an effective focal length (EFL) ranging from 0.2 mm to 2 mm. For example, the first microlens array 306 may include a pitch ranging from 300 μm and an EFL of 0.6 mm. When a collimated beam encounters this array, each individual microlens captures a portion of the light and focuses it into different small beams. The result is a grid-like pattern of small beams, each associated with a single microlens in the array.

[0060] In this case, the primary function of the microlens array is to ensure spatial uniformity of light intensity across the entire beam. This is achieved by effectively redistributing the light from the light source 302, thereby mitigating inhomogeneities or 'hot spots' within the beam. This beam uniformity is crucial for ensuring accurate projection of the test pattern onto the optical elements.

[0061] At operation 408, the purpose is to correct the incident angle of the beam. This is achieved by guiding the small beam from the first microlens array 306 onto the second microlens array 308. The second microlens array may include a pitch of approximately 300 μm and an EFL of 0.6 mm. The positioning of the second array corrects the direction of each small beam, thereby ensuring that the small beam is parallel to the optical axis. This prepares the small beam for projection onto a datum plate or microdisplay.

[0062] It is important to note that the correct incident angle of the beam at this stage significantly affects the quality and accuracy of the projection. An incorrect incident angle may cause distortion of the projected test pattern, which in turn affects the accuracy of the metrological measurements.

[0063] At operation 410, the process involves recolliding the beam. After correcting the incident angle of the beam at operation 408, the small beams are then realigned or 'recollided' to re-form a single coherent beam. This can be achieved, for example, by passing the beam through the second focusing lens 310. The role of this lens is to take the small beams separated and reoriented by the first microlens array 306 and the second microlens array 308, and to recombine these small beams into a unified beam parallel to the optical axis of the system. This step is desirable for maintaining the focus and parallelism of the beam as it continues to propagate through the optical system.

[0064] At operation 412, the re-collimated beam of light illuminates the grading plate or microdisplay to form the desired test pattern 312. The grading plate or microdisplay is a component that modulates the light transmitted through it to produce a specific pattern. This is achieved by blocking or transmitting light in specific areas, depending on the design of the test pattern. The patterns produced by the grading plate or microdisplay are typically nanometer-scale to ensure high accuracy.

[0065] When a beam of light passes through a caliper or microdisplay, the pattern interacts with the beam. This interaction imprints the pattern onto the beam, transforming it into a 'test pattern'. This test pattern is specifically designed to effectively test the performance of optical components. It can include various features such as line pairs, checkerboard patterns, or dot matrices, which can help evaluate different performance aspects of the optical component, such as its resolution, contrast, and chromatic aberration, among others.

[0066] At operation 414, a test pattern is projected onto a first grating 104a of an optical element 102 (such as an AR waveguide combiner) using a projection lens 314. The projection lens focuses the light carrying the test pattern and guides the light onto the optical element. In the case of an AR waveguide combiner, the light enters the waveguide through an input coupler.

[0067] Once inside the waveguide, the light carrying the test pattern travels along the waveguide via total internal reflection. Unbound by theory, this total internal reflection allows the light to remain trapped within the waveguide, enabling it to propagate potentially long distances without substantial loss. Waveguide properties, such as its physical dimensions, material composition, and internal structure, can modulate the light, thus affecting one or more of its intensity, phase, and polarization due to interaction with optical elements. The modulated light then exits the waveguide through the third grating 104c and is reflected toward the reflection detector 212.

[0068] By projecting test patterns onto optical elements, metrology tools lay the foundation for evaluating the performance of those elements. As the test patterns interact with the optical elements, they reveal valuable information about the performance characteristics of those elements, which will be captured and analyzed in subsequent operations.

[0069] At operations 416 and 418, camera lens 322 interacts with a reflection test pattern from the optical element. Specifically, in operation 416, camera lens 322 in the reflection detector picks up the reflection test pattern from the output coupler of the optical element. This light carries the test pattern along with any distortions or alterations imposed on it by the optical element.

[0070] Camera lens 322 focuses the reflected light and guides it toward the camera sensor within the reflection detector. The lens has been designed and positioned to ensure that it collects as much reflected light as possible and accurately focuses this light onto the camera sensor. The focal length of the camera lens has been selected to provide a larger field of view and high spatial resolution, thereby clearly capturing the details of the test pattern.

[0071] In operation 418, camera lens 322 projects a reflective test pattern onto camera 324. The optical design of the camera lens allows the test pattern to be accurately projected onto the camera sensor, thus preserving the spatial relationships within the pattern and any distortions imposed by the optical elements.

[0072] At operation 420, camera 324 receives and records the reflection test pattern. Camera 324, equipped with a CCD or CMOS sensor, captures an image of the reflected light carrying the test pattern. This image is a copy of the light that has interacted with the optical device and has undergone a transformation due to the nature of the optical elements themselves.

[0073] The recorded image data is then transmitted to controller 220 for processing and analysis. The processing and analysis of the recorded image data often employs advanced image processing algorithms and techniques. This process involves comparing the captured image of the reflection test pattern with the original pattern to determine if any differences exist. By analyzing these differences, the system can infer the optical performance and characteristics of the component under test.

[0074] In addition to the spatial properties of the image, camera 324 can also record other properties of reflected light, such as its intensity or color, which can provide additional information about the performance of the optical components. The system can use this data to calculate brightness uniformity, distortion, image sharpness, and other relevant metrics that define the quality of the optical components. The results of the analysis are reported, providing valuable feedback for the development, optimization, and quality control of the optical components. This information can be used to provide a thorough and accurate evaluation of the performance of the optical components.

[0075] Although the examples given above are specific to this disclosure, other and further examples of this disclosure may be devised without departing from the basic scope of this disclosure, which is defined by the appended claims.

Claims

1. An optical metrology system, the optical metrology system comprising: a light engine, the light engine comprising: a light source disposed above one or more micro-lens arrays; one or more focusing lenses disposed below the one or more micro-lens arrays, wherein the one or more focusing lenses are disposed above a reticle; and a projection lens having a first focal length disposed below the reticle, wherein the projection lens is configured to align with an input coupler of an optical element; and a reflective detector, the reflective detector comprising: a camera lens having a second focal length, wherein the camera lens is configured to align with an output coupler of the optical element; and a camera disposed above the camera lens, the camera configured to receive light from the camera lens, wherein the first focal length and the second focal length are different.

2. The optical metrology system of claim 1, wherein the first focal length is less than the second focal length.

3. The optical metrology system of claim 1, wherein the first focal length is about 10 mm to about 20 mm and the second focal length is about 20 mm to about 40 mm.

4. The optical metrology system of claim 1, wherein the light engine comprises a first focusing lens and a second focusing lens.

5. The optical metrology system of claim 4, wherein the first focusing lens is disposed above the one or more micro-lens arrays and the second focusing lens is disposed below the one or more micro-lens arrays.

6. The optical metrology system of claim 4, wherein the first focusing lens comprises a third focal length of about 10 mm to about 60 mm and the second focusing lens comprises a fourth focal length of about 10 mm to about 60 mm.

7. The optical metrology system of claim 1, wherein one or more micro-lens arrays comprise a first micro-lens array and a second micro-lens array.

8. The optical metrology system of claim 7, wherein the first micro-lens array comprises a fifth focal length of about 0.2 mm to about 2 mm and the second micro-lens array comprises a sixth focal length of 0.2 mm to 2 mm.

9. The optical metrology system of claim 1, further comprising a controller communicatively coupled to the light engine and the reflective detector, wherein the controller is configured to process a test pattern from the reflective detector.

10. An optical metrology system, the optical metrology system comprising: a light engine, the light engine comprising: a light source disposed above one or more micro-lens arrays; one or more focusing lenses disposed below the one or more micro-lens arrays, wherein the one or more focusing lenses are disposed above a reticle; and a projection lens having a first focal length disposed below the reticle, wherein the projection lens is configured to align with an input coupler of an optical element; and a reflective detector, the reflective detector comprising: a camera lens having a second focal length, wherein the camera lens is configured to align with an output coupler of the optical element; and a camera disposed above the camera lens, the camera configured to receive light from the camera lens, wherein the first focal length and the second focal length are different. a camera lens having a second focal length, wherein the camera lens is configured to align with an output coupler of the optical element; and a camera disposed above the camera lens, the camera configured to receive light from the camera lens, wherein the first focal length is about 10 mm to about 20 mm and the second focal length is about 20 mm to about 40 mm.

11. The optical metrology system of claim 10, wherein the light engine comprises a first focusing lens and a second focusing lens.

12. The optical metrology system of claim 11, wherein the first focusing lens is disposed above the one or more microlens arrays and the second focusing lens is disposed below the one or more microlens arrays.

13. The optical metrology system of claim 12, wherein the first focusing lens comprises a third focal length of about 10 mm to about 60 mm and the second focusing lens comprises a fourth focal length of about 10 mm to about 60 mm.

14. The optical metrology system of claim 10, wherein one or more microlens arrays comprise a first microlens array and a second microlens array.

15. The optical metrology system of claim 14, wherein the first microlens array comprises a fifth focal length of about 0.2 mm to about 2 mm and the second microlens array comprises a sixth focal length of 0.2 mm to 2 mm.

16. The optical metrology system of claim 10, further comprising a controller communicatively coupled to the light engine and the reflection detector, wherein the controller is configured to process a test pattern from the reflection detector.

17. A method, the method comprising: aligning a light engine with an input coupler of an optical element, the light engine comprising one or more microlens arrays, one or more focusing lenses disposed below the one or more microlens arrays, a reticle disposed below the one or more light concentrators, and a projection lens disposed below the reticle, wherein the projection lens comprises a first focal length; projecting a test pattern onto the optical element using the light engine; aligning a reflection detector with an output coupler of the optical element, the reflection detector comprising a camera lens and a camera disposed above the camera lens, wherein the camera lens comprises a second focal length, wherein the first focal length is less than the second focal length; receiving a reflected test pattern from the optical element using the reflection detector; and determining one or more metrology metrics of the optical element based on the reflected test pattern.

18. The method of claim 17, wherein the one or more metrology metrics comprise image sharpness, brightness uniformity, and distortion.

19. The method of claim 17, wherein projecting the test pattern comprises: modulating the test pattern based on one or more optical element properties.

20. The method of claim 19, wherein the one or more optical element properties comprise physical dimensions, material composition, and internal structure.

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