Modulation transfer function measurement apparatus and method for optical devices

Abstract

Embodiments herein provide a measurement system for determining the modulation transfer function (MTF) of an optical device. The measurement system includes a stage operable to hold either an optical device or an optical device substrate having at least one optical device disposed thereon. A light engine is disposed above the stage. The light engine includes a light source operable to project light of a range of wavelengths onto the optical device. The reticle is operable to form a pattern from the light projected from the light source. The first lens is operable to collimate the light from the light source toward the optical device or the optical device substrate. The near-field detector is operable to detect light from the optical device or the optical device substrate. The far-field detector is operable to detect light from the optical device or the optical device substrate.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to optical devices. More particularly, embodiments described herein provide methods and apparatus for determining the modulation transfer function (MTF) of an optical device. [Background technology]

[0002] Virtual reality is generally thought of as a computer-generated simulated environment in which a user has an apparent physical presence. Virtual reality experiences can be generated in 3D and viewed through a head-mounted display (HMD), such as glasses or other wearable display devices with near-eye display panels as lenses to display the virtual reality environment that replaces the real environment.

[0003] Augmented reality, on the other hand, enables an experience where a user still sees the surrounding environment through the display lenses of glasses or other HMD devices, but also sees images of virtual objects that are generated for display and appear as part of the environment. Augmented reality can include any type of input, such as audio and tactile input, as well as virtual images, graphics, and video that augment or augment the environment the user experiences. As an emerging technology, augmented reality has many challenges and design constraints.

[0004] One such challenge is determining the optical resolution of an optical device to ensure that image quality standards are met. Current measurement systems for optical devices typically have low sampling rates over a wide field of view, as well as low throughput, and are unable to adequately correct for image quality defects caused by the camera and image projector in the measurement system. Furthermore, the measurement systems can be bulky and susceptible to defects associated with the measurement system's image projector. Therefore, a system and method for optical resolution measurement that is not affected by defects associated with the image projector or camera and that improves throughput is desirable. Therefore, what is needed in the art is a method for determining the MTF of an optical device. Summary of the Invention

[0005] In one embodiment, a measurement system is provided. The measurement system includes a stage operable to hold either an optical device or an optical device substrate having at least one optical device disposed thereon, a light engine, a near-field detector, and a far-field detector. The light engine is disposed above the stage and includes a light source, a reticle operable to form a pattern from light projected from the light source, and a first lens operable to collimate the light from the light source toward the optical device or the optical device substrate. The light source is operable to project light of a range of wavelengths onto the optical device. The first lens is operable to collimate the light from the light source toward the optical device or the optical device substrate. The near-field detector is operable to detect light from the optical device or the optical device substrate. The far-field detector is operable to detect light from the optical device or the optical device substrate.

[0006] In another embodiment, a method is disclosed that includes projecting an image of a pattern, the image being projected from a light engine of a measurement system, projecting the image, capturing the near-field image at a near-field detector, capturing the far-field image at a far-field detector, analyzing the near-field image and the far-field image to locate a first plurality of points on the near-field image and the far-field image, the first plurality of points being transformed into a near-field function and a far-field function, obtaining a near-field fast Fourier transform (near-field FFT) of the near-field function and a far-field FFT of the far-field function, and determining an optical device modulation transfer function (MTF) of one or more optical devices, the optical device MTF being determined by comparing the near-field FFT corresponding to the image with the far-field FFT. The measurement system includes a stage disposed below the light engine, the stage operable to have the one or more optical devices disposed thereon. A light engine disposed above the stage projects the reference image onto one or more light devices, a near-field detector operable to detect light from the light devices, and a far-field detector operable to detect light from the light devices.

[0007] In yet another embodiment, a controller for a measurement system is disclosed. The controller stores instructions that, when executed by a processor, cause the measurement system to measure optical characteristics of an optical device of an optical device substrate disposed within the measurement system. The optical characteristics of the optical device or optical device substrate include projecting a reference image of a pattern. The reference image is projected from an optical engine of the measurement system. A near-field image is captured at a near-field detector of the measurement system. A far-field image is captured at a far-field detector of the measurement system. The near-field image and the far-field image are analyzed to identify locations of a first plurality of points on the near-field image and the far-field image. The first plurality of points are transformed into near-field and far-field functions. A near-field fast Fourier transform (near-field FFT) of the near-field function and a far-field FFT of the far-field function are obtained. An optical device modulation transfer function (MTF) of one or more optical devices is determined. The optical device MTF is determined by comparing the near-field FFT corresponding to the reference image with the reference far-field FFT.

[0008] In order that the above-listed features of the present disclosure may be understood in detail, a more particular description of the present disclosure briefly summarized above can be made with reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only exemplary embodiments and therefore should not be considered as limiting its scope, admitting of other equally effective embodiments. [Brief explanation of the drawings]

[0009] [Figure 1A] FIG. 1 is a front general view of a substrate according to embodiments described herein. [Figure 1B] 1 is a front general view of an optical device according to embodiments described herein. [Figure 2] 1 is a schematic cross-sectional view of a measurement system according to embodiments described herein. [Figure 3A] FIG. 1 is a schematic diagram of a measurement system for determining the modulation transfer function (MTF) of an optical device according to embodiments described herein. [Figure 3B] FIG. 1 is a schematic diagram of a measurement system for determining the modulation transfer function (MTF) of an optical device according to embodiments described herein. [Figure 3C] FIG. 1 is a schematic diagram of a measurement system for determining the modulation transfer function (MTF) of an optical device according to embodiments described herein. [Figure 3D] FIG. 1 is a schematic diagram of a measurement system for determining the modulation transfer function (MTF) of an optical device according to embodiments described herein. [Figure 3E] FIG. 1 is a schematic diagram of a measurement system for determining the modulation transfer function (MTF) of an optical device according to embodiments described herein. [Figure 4] FIG. 1 is a flow diagram of a method for determining the modulation transfer function (MTF) of an optical device according to embodiments described herein. DETAILED DESCRIPTION OF THE INVENTION

[0010] For ease of understanding, where possible, the same reference numerals are used to designate identical elements that are common to multiple figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0011] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to optical devices. More particularly, embodiments described herein provide a method for determining the modulation transfer function (MTF) of an optical device.

[0012] 1A is a front general view of a substrate 101 according to embodiments described herein. The substrate 101 includes a plurality of optical devices 100 disposed on a surface 103 of the substrate 101. The optical devices 100 are waveguide couplers used in virtual reality, augmented reality, or mixed reality. In some embodiments, which can be combined with other embodiments described herein, the optical devices 100 are planar optical devices, such as metasurfaces.

[0013] Substrate 101 can be any substrate used in the art and can be either opaque or transparent to the selected laser wavelength, depending on the application of substrate 101. Furthermore, the shape, thickness, and diameter of substrate 101 can vary. For example, substrate 101 can have a diameter of about 150 mm to about 300 mm. Substrate 101 can have a circular, rectangular, or square shape. Substrate 101 can have a thickness between about 300 μm and about 1 mm. Although only nine optical devices 100 are shown on substrate 101, any number of optical devices 100 can be disposed on surface 103.

[0014] FIG. 1B illustrates a front view of an optical device 100. It should be understood that the optical device 100 described herein is an exemplary optical device, and that other optical devices having or modified to achieve aspects of the present disclosure may be used. The optical device 100 includes a plurality of optical device structures 102 disposed on a surface 103 of a substrate 101. The optical device structures 102 may be nanostructures having submicron dimensions, e.g., nano-sized dimensions. Regions of the optical device structures 102 correspond to one or more gratings 104, such as a first grating 104a, a second grating 104b, and a third grating 104c. In some embodiments that can be combined with other embodiments described herein, the optical device 100 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, which may be combined with other embodiments described herein, the optical device 100 also includes a second grating 104b corresponding to the intermediate grating. The optical device structure 102 may be angular or binary. The optical device structure 102 may have other shapes, including, but not limited to, circular, triangular, elliptical, regular polygonal, irregular polygonal, and / or irregularly shaped cross sections.

[0015] In operation, the first grating 104a receives an incident light beam (virtual image) from a light source having a certain intensity. To direct the virtual image to the intermediate grating (if utilized) or the third grating 104c, the incident beam is split by the optical device structure 102 into a T1 beam having all of the intensity of the incident beam. In some embodiments, which can be combined with other embodiments described herein, the T1 beam undergoes total internal reflection (TIR) ​​through the optical device 100, until the T1 beam contacts the intermediate grating optical device structure 102. The intermediate grating optical device structure 102 diffracts the T1 beam into a T-1 beam, which TIRs through the optical device 100 to the optical device structure 102 of the third grating 104c. The optical device structure 102 of the third grating 104c output couples the T-1 beam into the user's eye, adjusting the field of view of the virtual image generated from the light source from the user's viewpoint and further increasing the viewing angle at which the user can view the virtual image. In some embodiments, which can be combined with other embodiments described herein, the T1 beam undergoes TIR through the optical device 100, and eventually the T1 beam contacts the optical device structure 102 of the third grating 104c and is output coupled to adjust the field of view of the virtual image generated from the light source.

[0016] The optical device MTF of the optical device 100 is obtained to ensure that the optical device 100 meets image quality standards. In some embodiments, the optical device MTF provides image quality information related to image resolution and image contrast. The embodiments of the measurement system 200 described herein provide the ability to obtain the optical device MTF with improved throughput and greater quality control. Furthermore, the embodiments of the measurement system 200 described herein provide the ability to obtain the optical device MTF such that the measured optical device MTF is not strongly affected by imperfections of the image projector and / or camera, such as distortion and astigmatism. The embodiments described herein enable a separation between the image quality of the optical device 100 and the image quality of the measurement system 200, which may include imperfections that may be solely attributable to the camera or projector. The MTF is a metric utilized to determine the ability of the optical device 100 to transfer contrast from an object to an image at a particular resolution.

[0017] 2 is a schematic cross-sectional view of a measurement system 200 according to an embodiment described herein. The measurement system 200 includes a body 201 having a first opening 203 and a second opening 205 to allow a stage 207 to move therethrough. The stage 207 is operable to move in the X, Y, and Z directions within the body 201 of the measurement system 200. The stage 207 includes a tray 209 operable to hold either an optical device 100 (shown herein) or one or more substrates 101.

[0018] Measurement system 200 is operable to project an image so that the MTF of optical device 100 can be determined. Stage 207 and tray 209 may be transparent so that the MTF obtained using measurement system 200 is not affected by the translucency of stage 207 or tray 209. Measurement system 200 is in communication with controller 220 operable to control the operation of measurement system 200 and methods 400 described herein.

[0019] Measurement system 200 includes an upper portion 204 oriented above optical device 100 and a lower portion 206 oriented below optical device 100. Upper portion 204 of measurement system 200 includes an alignment camera 208, a light engine 210, and a reflective detector 212. Reflective detector 212 detects the outcoupled beam projected from third grating 104c above optical device 100. Reflective detector 212 includes a near-field detector, a far-field detector, a wave sensor, or a combination thereof. Reflective detector 212 of measurement system 200a and measurement system 200c includes near-field detector 320. Near-field detector 320 is operable to capture an image of the outcoupled beam at a pupil plane of third grating 104c of measurement system 200a. By capturing an image of the outcoupled beam at the pupil plane of the third grating 104c, measurement system 200a can image the outcoupled beam in the third grating 104c. Reflective detector 212 of measurement system 200c further includes a lens 322 for focusing the outcoupled beam toward near-field detector 320 when near-field detector 320 is not in the pupil plane. Reflective detector 212 of measurement systems 200b and 200e includes a near-field detector 310. Far-field detector 310 is operable to capture an image of the outcoupled beam at a display location where the image will be projected. Reflective detector 212 of measurement system 200d includes a wavefront sensor 325. Wavefront sensor 325 is operable to capture an image of the outcoupled beam at the pupil plane of the third grating 104c of measurement system 200d. By capturing an image of the output coupled beam at the pupil plane of the third grating 104c, the measurement system 200d can image the output coupled beam before distortion and dispersion occur to the output coupled beam as it propagates towards the display.

[0020] Transmission detector 216 detects the outcoupled beam projected from third grating 104c through below optical device 100. Transmission detector 216 includes a near-field detector, a far-field detector, a wavefront sensor, or a combination thereof. Transmission detector 216 of measurement system 200a and measurement system 200c includes far-field detector 310. Far-field detector 310 is operable to capture an image of the outcoupled beam at the location of the display where the image will be projected. Transmission detector 216 of measurement system 200b includes near-field detector 320. Near-field detector 320 is operable to capture an image of the outcoupled beam at the pupil plane of third grating 104c of measurement system 200b. By capturing an image of the outcoupled beam at the pupil plane of third grating 104c, measurement system 200b can image the outcoupled beam before it is distorted and dispersed as it propagates toward the display. Transmission detector 216 of measurement system 200e includes a wavefront sensor 325. Wavefront sensor 325 is operable to capture an image of the outcoupled beam at a pupil plane of third grating 104c of measurement system 200e. By capturing an image of the outcoupled beam at the pupil plane of third grating 104c, measurement system 200e can image the outcoupled beam before it is distorted and dispersed as it propagates toward the display.

[0021] Alignment camera 208 is operable to determine the position of stage 207 and optical device 100. Light engine 210 is operable to illuminate first grating 104a. In some embodiments, which may be combined with other embodiments described herein, light engine 210 projects an image of a pattern onto first grating 104a.

[0022] The lower portion 206 of the first subsystem 202 includes a code reader 214 and a transmission detector 216. The code reader 214 is operable to read a code on the optical device, such as a quick response (QR) code or a barcode on the optical device 100. The code read by the code reader 214 may include instructions for obtaining the optical device MTF for various optical devices 100.

[0023] The controller 220 is coupled to the measurement system 200. The controller 220 includes a processor 252, a memory 254, and support circuits 256, which are coupled to each other. The controller 220 is electrically coupled to the measurement system 200 via electrical lines 258, which may represent a wireless connection in some embodiments. The processor 252 may be one of any form of general-purpose microprocessor or general-purpose central processing unit (CPU), each of which may 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. The memory 254 is non-transitory and may be one or more of readily available memory, such as random access memory (RAM), read-only memory (ROM), or any other form of digital storage, local or remote. The memory 254 includes instructions that, when executed by the processor 252, facilitate the execution of the method 400. The instructions in the memory 254 are in the form of a program product, such as a program that implements the methods of the present disclosure. The program code of the program product may conform to any one of several different programming languages. Exemplary computer-readable storage media include, but are not limited to: (i) non-writable storage media in which information is permanently stored (e.g., a read-only memory device in a computer, such as a CD-ROM disk readable in a CD-ROM drive, a flash memory, a ROM chip, or any type of solid-state non-volatile semiconductor memory), and (ii) writable storage media in which changeable information is stored (e.g., a floppy disk in a diskette drive or hard disk drive, or any type of solid-state random-access semiconductor memory). Such computer-readable storage media, when carrying computer-readable instructions that direct the functions of the methods described herein, are examples of the present disclosure.

[0024] 3A-3E are schematic diagrams of measurement systems 200a-200e. Measurement systems 200a-200e can be used in a method 400 for determining optical device MTF. Measurement system 200 includes a light engine 210, a transmission detector 216, and a reflection detector 212. Light engine 210 includes a light source 302, a reticle 304, and a first lens 306. Light engine 210 can further include at least one of a quarter-wave plate or a linear polarizer. In some embodiments, which may be combined with other embodiments described herein, light source 302 is configured to project red light (wavelengths of about 610 nm to about 660 nm), green light (wavelengths of about 510 nm to about 560 nm), and blue light (wavelengths of about 420 nm to about 470 nm). Reticle 304 can be a display.

[0025] In one embodiment, as shown in measurement system 200a in FIG. 3A , transmission detector 216 includes a far-field detector 310. Far-field detector 310 is operable to detect the outcoupled beam projected from third grating 104c through a path below optical device 100 to form a far-field image. Second lens 308 is operable to focus the outcoupled image toward far-field detector 310. Far-field detector 310 captures the far-field image, in which some optical data may be missing due to imperfections in the MTF of optical device 100. Reflection detector 212 includes a near-field detector 320. Near-field detector 320 is operable to detect the outcoupled beam projected from third grating 104c through a path above optical device 100 to form a near-field image. In some embodiments, the near field detector 320 is positioned less than about 3 mm from the third grating 104c of the optical device 100, such as less than about 1 mm from the third grating 104c of the optical device 100. The near field detector 320 is positioned as close as possible to the third grating 104c of the optical device 100 to minimize the amount of optical data lost due to an MTF impairment of the optical device 100. The near field image captured at the near field detector 320 and the far field image captured at the far field detector 310 are operable to be compared to determine whether an MTF impairment has occurred.

[0026] In another embodiment, as shown in measurement system 200b in FIG. 3B , reflection detector 212 includes a far-field detector 310. Far-field detector 310 is operable to detect the outcoupled beam projected from third grating 104c above optical device 100 to form a far-field image. Second lens 308 is operable to focus the outcoupled image toward far-field detector 310. Far-field detector 310 captures the far-field image, in which some optical data may be missing due to imperfections in the MTF of optical device 100. Transmission detector 216 includes a near-field detector 320. Near-field detector 320 is operable to detect the outcoupled beam projected from third grating 104c below optical device 100 to form a near-field image. In some embodiments, the near field detector 320 is positioned less than about 3 mm from the third grating 104c of the optical device 100, such as less than about 1 mm from the third grating 104c of the optical device 100. The near field detector 320 is positioned as close as possible to the third grating 104c of the optical device 100 to minimize the amount of optical data lost due to an MTF impairment of the optical device 100. The near field image captured at the near field detector 320 and the far field image captured at the far field detector 310 are operable to be compared to determine whether an MTF impairment has occurred.

[0027] In another embodiment, as shown in measurement system 200c in FIG. 3C , transmission detector 216 includes a far-field detector 310. Far-field detector 310 is operable to detect the outcoupled beam projected from third grating 104c through a path below optical device 100 to form a far-field image. Second lens 308 is operable to focus the outcoupled image toward far-field detector 310. Far-field detector 310 captures the far-field image, in which some optical data may be lost due to imperfections in the MTF of optical device 100. Reflection detector 212 includes near-field detector 320. Near-field detector 320 is operable to detect the outcoupled beam projected from third grating 104c through a path above optical device 100 to form a near-field image. A third lens 322 is disposed between third gratings 104c. The third lens 322 is positioned less than about 3 mm from the third grating 104c of the optical device 100, for example, less than about 1 mm from the third grating 104c of the optical device 100. The third lens 322 is positioned as close as possible to the third grating 104c of the optical device 100 to minimize the amount of optical data lost due to MTF impairments of the optical device 100. The third lens 322 is operable to focus the near-field image toward the near-field detector 320. The near-field detector 320 is disposed about 10 mm to about 50 mm from the third grating 104c. The near-field image captured at the near-field detector 320 and the far-field image captured at the far-field detector 310 are operable to be compared to determine whether an MTF impairment has occurred.

[0028] In another embodiment, as shown in measurement system 200d in FIG. 3D , transmission detector 216 includes a far-field detector 310. Far-field detector 310 is operable to detect the outcoupled beam projected from third grating 104c through a path below optical device 100 to form a far-field image. Second lens 408 is operable to focus the outcoupled image toward far-field detector 310. Far-field detector 310 captures an image in which some optical data may be missing due to imperfections in the MTF of optical device 100. Reflection detector 212 is a wavefront sensor 325. Wavefront sensor 325 is operable to detect the outcoupled beam projected from third grating 104c through a path above optical device 100 to form a near-field image. In some embodiments, the wavefront sensor 325 is positioned less than about 3 mm from the third grating 104c of the optical device 100, for example less than about 1 mm from the third grating 104c of the optical device 100. The wavefront sensor 325 is positioned as close as possible to the third grating 104c of the optical device 100 to minimize the amount of optical data lost due to MTF impairments of the optical device 100. The near-field image captured at the wavefront sensor 325 and the far-field image captured at the far-field detector 310 are operable to be compared to determine whether an MTF impairment has occurred. The wavefront sensor 325 can further measure the phase (e.g., direction) of the light in the image.

[0029] In another embodiment, as shown in measurement system 200e of FIG. 3E , reflection detector 212 includes a far-field detector 310. Far-field detector 310 is operable to detect the outcoupled beam projected from third grating 104c above optical device 100 to form a far-field image. Second lens 308 is operable to focus the outcoupled image toward far-field detector 310. Far-field detector 310 captures the far-field image, in which some optical data may be missing due to imperfections in the MTF of optical device 100. Transmission detector 216 is a wavefront sensor 325. Wavefront sensor 325 detects the outcoupled beam projected from third grating 104c below optical device 100 to form a near-field image. In some embodiments, the wavefront sensor 325 is positioned less than about 3 mm from the third grating 104c of the optical device 100, for example less than about 1 mm from the third grating 104c of the optical device 100. The wavefront sensor 325 is positioned as close as possible to the third grating 104c of the optical device 100 to minimize the amount of optical data lost due to MTF impairments of the optical device 100. The near-field image captured at the wavefront sensor 325 and the far-field image captured at the far-field detector 310 are operable to be compared to determine whether an MTF impairment has occurred. The wavefront sensor 325 can further measure the phase (e.g., direction) of the light in the image.

[0030] 4 is a flow diagram of a method 400 for determining the optical device MTF. Method 400 is operable to be performed in other measurement systems not described herein. Method 400 described herein includes illuminating first grating 104a of optical device 100 using light engine 210, where in-coupled (e.g., reflected or transmitted) light from third grating 104c undergoes TIR and is ultimately out-coupled as an image captured by transmission detector 216 and reflection detector 212. The image may correspond to red, green, and blue channels from light engine 210. The image is processed as described in method 400 to extract the MTF of optical device 100.

[0031] In operation 401, a reference image is projected toward the optical device 100 using the light engine 210 of the measurement system 200. The reference image is projected after the light source 302 projects red, green, or blue light through the reticle 304 to form a pattern. The reference image relates to the pattern. In some embodiments that can be combined with other embodiments described herein, the light engine 210 is a high-resolution image projector having a field of view (FOV) of about 10 degrees to about 120 degrees. The FOV of the light engine 210 is fixed or adjustable. The pattern is determined by the reticle 304. The reticle 304 can have one of a grating pattern, a line pair pattern, or a dot matrix pattern. In some embodiments that can be combined with other embodiments described herein, the reticle 304 is a high-resolution patterned mask. The pattern of the reticle 304 can be formed by an electron beam, an ion beam, or photolithography. In other embodiments that can be combined with other embodiments described herein, the light engine 210 is one of an LCOS, CLP, micro light emitting diode (micro LED), laser beam scanner, or organic light emitting diode (OLED) micro display.

[0032] The pattern is projected onto the first grating 104a through a first lens 306. The first lens 306 focuses the pattern toward the first grating 104a. The pattern undergoes TIR through the optical device 100, and finally, the pattern is output coupled from the third grating 104c. In some embodiments that can be combined with other embodiments described herein, the optical device 100 can include a surface-relief grating-based waveguide coupler, a volume hologram-based waveguide coupler, a birdbath waveguide coupler, a partially reflective mirror array coupler, or a free-from-optics combiner. The pattern is determined by a reticle 304. The reticle 304 can have one of a grating pattern, a line pair pattern, or a dot matrix pattern. In some embodiments that can be combined with other embodiments described herein, the reticle 304 is a high-resolution patterned mask.

[0033] In operation 402, images are captured at reflection detector 212 and transmission detector 216. The images are of a pattern formed by reticle 304. In some embodiments, which may be combined with other embodiments described herein, transmission detector 216 includes far-field detector 310, near-field detector 320, wavefront sensor 325, or a combination thereof. In some embodiments, reflection detector 212 includes far-field detector 310, near-field detector 320, wavefront sensor 325, or a combination thereof. Near-field detector 320 or wavefront sensor 325 detects a near-field image of the pattern formed by the reticle. The near-field image is captured at or near the pupil plane of third grating 104c, thereby minimizing optical data lost due to potential MTF imperfections in optical device 100. Far-field detector 310 detects the far-field image at a distance approximately equal to the display distance of optical device 100 (e.g., the distance at which the optical device will project an image so that it is visible to a user of the optical device). Any potential MTF failure will result in distorted / degraded far field images.

[0034] In operation 403, the near-field image and the far-field image are analyzed. In some embodiments, which may be combined with other embodiments described herein, the near-field image and the far-field image are analyzed to identify the location of a plurality of points on the near-field image and the far-field image. Each of the plurality of points may correspond to a different FOV across the near-field image and the far-field image. For example, each of the plurality of points may correspond to adjacent square edges in a grating pattern. The plurality of points are transformed into near-field and far-field functions according to the formed pattern. For example, the functions may be a point spread function, a line spread function, or an edge spread function.

[0035] In operation 404, a near-field function MTF of the near-field function and a far-field function MTF of the far-field function are obtained. To properly obtain the function MTF corresponding to the reference image, it is necessary to minimize the variation in light intensity across the image. The variation in light intensity across the image can be reduced by adjusting the exposure time of the image. The exposure time can be adjusted for each of multiple points of the near-field function and the far-field function.

[0036] In operation 405, the optical device MTF is obtained. By correlating the near-field and far-field images using multiple points and functions, MTF performance can be measured and defects can be detected. Furthermore, degradation of the pupil function along the propagation in the third grating 104c can be detected. In this way, the cause of the MTF defect can be detected. The optical device MTF obtained using method 400 is less susceptible to defects in the light engine 210.

[0037] In summary, a method and apparatus for determining the MTF of an optical device are described herein. The apparatus includes a measurement system including a stage operable to hold either an optical device or an optical device substrate having at least one optical device disposed thereon. A light engine is disposed above the stage. The light engine includes a light source operable to project light of a range of wavelengths onto the optical device. The reticle is operable to form a pattern from the light projected from the light source. A near-field detector is operable to detect light from the optical device or optical device substrate at a pupil plane of the optical device. A far-field detector is operable to detect light from the optical device or optical device substrate at a display distance of the optical device. Images of the light detected at the far-field detector and the near-field detector are compared to determine the MTF of the optical device substrate or optical device. Causes of MTF defects can be further detected by the measurement system.

[0038] While the forgoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, which scope is determined by the following claims.

Claims

1. a stage operable to hold either an optical device or an optical device substrate having at least one optical device disposed thereon; a light engine disposed above the stage, a light source operable to project light of a range of wavelengths onto said optical device; a reticle operable to form a pattern from the light projected from the light source; and a light engine including a first lens operable to collimate the light from the light source toward the optical device or the optical device substrate; a near field detector operable to detect the light from the optical device or the optical device substrate; a far field detector operable to detect the light from the optical device or the optical device substrate; A measurement system comprising:

2. The measurement system of claim 1 , wherein the near-field detector is positioned above the optical device or the optical device substrate, and the far-field detector is positioned below the optical device or the optical device substrate.

3. The measurement system of claim 1 , wherein the near-field detector is disposed below the optical device or the optical device substrate, and the far-field detector is disposed above the optical device or the optical device substrate.

4. The measurement system of claim 1 , wherein the near-field detector is a wavefront sensor.

5. The measurement system of claim 1 , wherein the stage is operable to move in X, Y, and Z directions.

6. The measurement system of claim 1 , wherein the stage is transparent.

7. The measurement system of claim 1 , further comprising an alignment camera operable to determine the position of the stage and the optical device or the optical device substrate.

8. projecting a reference-reference image of the pattern, the reference-reference image being projected from a light engine of a measurement system, the measurement system comprising: a stage disposed below the light engine, the stage operable to have one or more light devices disposed on the stage, the light engine disposed above the stage projecting the reference image onto the one or more light devices; and a near field detector operable to detect the light from the optical device; and projecting a reference image of a pattern having a far field detector operable to detect the light from the optical device; acquiring a near field image at the near field detector; acquiring a far-field image at the far-field detector; analyzing the near field image and the far field image to locate a first plurality of points on the near field image and the far field image, the first plurality of points being transformed into a near field function and a far field function; obtaining a near-field fast Fourier transform (near-field FFT) of the near-field function and a far-field fast Fourier transform (far-field FFT) of the far-field function; determining an optical device modulation transfer function (optical device MTF) of the one or more optical devices, the optical device MTF being determined by comparing the near-field FFT corresponding to the reference image with the far-field FFT; A method comprising:

9. The method of claim 8 , wherein the near-field detector is positioned above the optical device or optical device substrate, and the far-field detector is positioned below the optical device or optical device substrate.

10. The method of claim 8 , wherein the near-field detector is located below the optical device or the optical device substrate, and the far-field detector is located above the optical device or the optical device substrate.

11. The method of claim 8 , wherein the near-field detector is a wavefront sensor.

12. The method of claim 8 , wherein the reference image is projected through a reticle to form the pattern.

13. 10. The method of claim 8, wherein the field of view of the light engine is from about 10 degrees to about 120 degrees.

14. The method of claim 8 , wherein the stage is operable to move in X, Y, and Z directions.

15. 1. A measurement system controller storing instructions that, when executed by a processor, cause the measurement system to measure an optical property of an optical device or optical device substrate disposed within the measurement system, the optical property of the optical device or the optical device substrate comprising: projecting a reference image of a pattern, the reference image being projected from a light engine of the measurement system; acquiring a near field image at a near field detector of the measurement system; acquiring a far-field image at a far-field detector of the measurement system; analyzing the near field image and the far field image to locate a first plurality of points on the near field image and the far field image, the first plurality of points being transformed into a near field function and a far field function; obtaining a near-field fast Fourier transform (near-field FFT) of the near-field function and a far-field fast Fourier transform (far-field FFT) of the far-field function; determining an optical device modulation transfer function (optical device MTF) of one or more optical devices, the optical device MTF being determined by comparing the near-field FFT corresponding to the reference image with the far-field FFT.

16. The controller of claim 15 , wherein the reference image is projected through a reticle to form the pattern.

17. The controller of claim 15 , wherein the near field detector is located above the optical device or the optical device substrate, and the far field detector is located below the optical device or the optical device substrate.

18. The controller of claim 15 , wherein the near field detector is located below the optical device or the optical device substrate, and the far field detector is located above the optical device or the optical device substrate.

19. The controller of claim 15 , wherein the near field detector is a wavefront sensor.

20. 16. The controller of claim 15, wherein the field of view of the light engine is from about 10 degrees to about 120 degrees.

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