Full-field metrology tools for waveguide combiners and metasurfaces

Abstract

The embodiments described herein provide a metrology tool and method for acquiring a full field optical field of an optical device to determine a number of metrology metrics of the optical device. The metrology tool is utilized to split a light beam into a first light path and a second light path. The first light path and the second light path are superimposed into a superimposed light beam and sent to a detector. The detector measures the intensity of the superimposed light beam. The first and second equations are utilized in combination with the intensity measurements to determine the amplitude and phase ip at a reference point directly adjacent to the second surface of the at least one optical device.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to metrology tools. More particularly, embodiments described herein provide metrology tools and methods for acquiring the full-field optical field of an optical device to determine multiple metrology metrics of the optical device. [Background technology]

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

[0003] However, augmented reality allows for an experience in which a user can still look through the display lenses of glasses or other HMD devices to view the surrounding environment and also see images of virtual objects that are generated for display and appear as part of that environment. Augmented reality can include any type of input, such as audio and haptic input, as well as virtual images, graphics, and video, that enhances or augments the environment the user experiences. As an emerging technology, there are many challenges and design constraints for augmented reality.

[0004] One such challenge is obtaining a complete characterization of an optical device used for virtual reality and augmented reality. Metrology metrics need to be measured to ensure that optical device designs are verified and optical device metrology metrics are monitored. To obtain the metrology metrics, multiple metrology tools are utilized to determine different metrics, which can be time-consuming, inefficient, and costly. When obtaining metrology metrics, it is desirable to have a measurement method that is overall high, low cost, and has low bandwidth requirements. Therefore, a single metrology tool and method that can obtain a complete characterization of an optical device is desirable. Therefore, what is needed in the art is a metrology tool and method that obtains the full field of view optical field of an optical device to determine multiple metrology metrics of the optical device. Summary of the Invention

[0005] In one embodiment, a metrology tool is provided. The metrology tool includes an optical engine operable to project a light beam. The metrology tool further includes a first beam splitter disposed in a path of the light beam. The first beam splitter is operable to split the light beam into a first light path and a second light path, the first light path being operable to enter an optical device. The metrology tool further includes a phase modulator disposed in the second light path. The metrology tool further includes a second beam splitter disposed in the first light path and the second light path. The second beam splitter is operable to overlap the first light path and the second light path to form a overlapped light path. The metrology tool further includes a detector disposed in the overlapped light path. The detector is operable to record an intensity of the overlapped light path.

[0006] In another embodiment, a metrology tool is provided. The metrology tool includes an optical engine operable to project a light beam. The metrology tool further includes a first beam splitter disposed in a path of the light beam. The first beam splitter is operable to split the light beam into a first light path and a second light path. The first light path is operable to be incident on an optical device. The metrology tool further includes a modulation module disposed in the first light path. The modulation module is operable to change the phase, amplitude, or angle of incidence of the first light path. The metrology tool further includes a tilt mirror disposed in the second light path and a second beam splitter disposed in the first light path and the second light path. The second beam splitter is operable to overlap the first light path and the second light path to form a overlapped light path. The metrology tool further includes a detector disposed in the overlapped light path. The detector is operable to record the intensity of the overlapped light path.

[0007] In yet another embodiment, a method is provided. The method includes projecting a light beam onto a first beam splitter. The first beam splitter splits the light beam into a first light path and a second light path. The method further includes projecting the first light path onto an optical device. The first light path travels through the optical device. The optical device is a metasurface or a waveguide combiner. The method further includes projecting the second light path onto a phase modulator. The phase modulator is operable to generate one or more phase-delayed images of the second light path. The method further includes overlapping the first light path and the second light path with a second beam splitter to form a overlapped light path. The method further includes directing the overlapped light path to a detector. The detector is operable to record intensity measurements of the first light path and the second light path. The method further includes determining a full-field optical field of the optical device at a reference point located adjacent a surface of the optical device where the first optical path exits the optical device, the full-field optical field being determined by performing a Fourier transform on the intensity measurements to reconstruct the amplitude and phase of the first optical path at the reference point.

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

[0009] [Figure 1] 1 is a schematic cross-sectional view of a metrology tool according to an embodiment described herein. [Figure 2] 1 is a schematic cross-sectional view of a metrology tool according to an embodiment described herein. [Figure 3]1 is a flow diagram of a method for determining a full-field optical field of at least one optical device according to embodiments described herein. DETAILED DESCRIPTION OF THE INVENTION

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

[0011] Embodiments of the present disclosure generally relate to metrology tools. More particularly, embodiments described herein provide a metrology tool and method for acquiring a full-field optical field of an optical device to determine multiple metrology metrics of the optical device. The metrology tool includes an optical engine operable to project a light beam. The metrology tool further includes a first beam splitter disposed in a path of the light beam. The first beam splitter is operable to split the light beam into a first light path and a second light path, the first light path being operable to enter the optical device. The metrology tool further includes a phase modulator disposed in the second light path. The metrology tool further includes a second beam splitter disposed in the first light path and the second light path. The second beam splitter is operable to overlap the first light path and the second light path to form a overlapped light path. The metrology tool further includes a detector disposed in the overlapped light path. The detector is operable to record an intensity of the overlapped light path.

[0012] FIG. 1 is a schematic cross-sectional view of a metrology tool 100. In a first embodiment of the metrology tool 100, the metrology tool 100 includes a third lens 122A and a fourth lens 122B. In a second embodiment of the metrology tool 100, the metrology tool 100 includes a fifth lens 124. The metrology tool 100 includes a phase modulator 120. In a first configuration of the phase modulator 120, the phase modulator 120 is a spatial light modulator. In a second configuration of the phase modulator 120, the phase modulator 120 is a piezo-driven mirror. In a third configuration of the phase modulator 120, the phase modulator 120 is a tilting mirror. Either the first or second embodiment of the metrology tool 100 includes at least one of the phase modulator 120 in the first, second, or third configurations.

[0013] The metrology tool 100 is operable to hold a substrate 108. The substrate 108 includes at least one optical device 102 disposed thereon. The substrate 108 may be any substrate used in the art and may be either opaque or transparent to a selected wavelength, depending on the use of the substrate 108. Furthermore, the substrate 108 may be of various shapes, thicknesses, and diameters. The substrate 108 may have a circular, rectangular, or square shape. The substrate 108 is not limited in the number of optical devices 102 that may be disposed thereon. Each optical device 102 may include multiple optical device structures disposed thereon. The optical device structures may be nanostructures having submicron dimensions, e.g., nano-sized dimensions.

[0014] It should be understood that the at least one optical device 102 described herein is an exemplary optical device, and that other optical devices may be used with or modified to achieve aspects of the present disclosure. In one embodiment that may be combined with other embodiments described herein, the optical device 102 is a waveguide combiner. Waveguide combiners may be utilized for virtual reality, augmented reality, or mixed reality. In an embodiment in which the optical device 102 is a waveguide combiner, an input coupling region may be disposed on a first surface 104 of the optical device 102. An output coupling region may be disposed on a second surface 106 of the optical device 102. The second surface 106 is on a surface opposite the first surface 104. In another embodiment that may be combined with other embodiments described herein, the waveguide combiner includes an input coupling region and an output coupling region on the same surface, for example, on one of the first surface 104 or the second surface 106. In yet another embodiment, which may be combined with other embodiments described herein, the optical device 102 is a planar optical device, such as a metasurface, including, but not limited to, one of a lens, a diffuser, a dot matrix projector, or a sensor.

[0015] The metrology tool 100 is operable to measure the full-field optical field of at least one optical device 102. The methods described herein improve throughput, reduce storage and bandwidth requirements, and reduce costs associated with analyzing optical devices. The full-field optical field includes the amplitude and phase of light rays. The full-field optical field provides direct information of the optical device 102 by measuring the full-field optical field in parallel. Metrology metrics can be obtained from the full-field optical field to ensure the design of the optical device 102 is verified and optical device metrology metrics are monitored. Embodiments of the metrology tool 100 described herein provide the ability to obtain multiple metrology metrics with increased throughput. The metrology metrics include one or more of an angular uniformity metric, a contrast metric, an efficiency metric, a color uniformity metric, a modulation transfer function (MTF) metric, a field of view (FOV) metric, a ghost image metric, or an eyebox metric for a waveguide combiner. The metrology metrics include one or more of an efficiency metric, a point spread function (PSF) metric, or a phase error metric for a metasurface.

[0016] The metrology tool 100 includes a light engine 110, a first beam splitter 112, a second beam splitter 114, a mirror 116, a third beam splitter 118, a phase modulator 120, a first lens 126, and a detector 128. In some embodiments, which may be combined with other embodiments described herein, the metrology tool 100 includes one or more of a linear polarizer 130, a second lens 132, a pinhole 134, and an auxiliary lens 142. In a first embodiment of the metrology tool 100, the metrology tool 100 includes a third lens 122A and a fourth lens 122B. In a second embodiment of the metrology tool 100, the metrology tool 100 includes a fifth lens 124.

[0017] The light engine 110 is operable to project a light beam onto the first beam splitter 112. In one embodiment, which may be combined with other embodiments described herein, the light engine 110 is a light emitting diode (LED) or a laser. In another embodiment, which may be combined with other embodiments described herein, the light engine 110 includes a display module. The display module is operable to project a pattern onto the optical device 102. The display module may include a micro LED module, a liquid crystal on silicon (LCOS) module, a digital light processing (DLP) module, or a laser projection module. In yet another embodiment, which may be combined with other embodiments described herein, the light beam is incident on a linear polarizer 130 before contacting the first beam splitter 112. The linear polarizer 130 is operable to linearly polarize the incoming light beam. The linear polarizer 130 may be a half-wave plate.

[0018] A first beam splitter 112 splits the light beam into a first optical path 136A and a second optical path 136B. The optical device 102 is disposed in the first optical path 136A. The optical device 102 may be any suitable optical device, such as a waveguide combiner or a metasurface. The first optical path 136A is directed toward the optical device 102 to be measured. The first optical path 136A is incident on a first surface 104 of the optical device 102. In some embodiments, a modulation module 113 is disposed adjacent to the first surface 104. The modulation module 113 is operable to change the phase, amplitude, or angle of incidence of the first optical path 136A.

[0019] In an embodiment in which the optical device 102 is a waveguide combiner, as shown in FIG. 1 , the first optical path 136A enters the input coupling region. The first optical path 136A passes through the waveguide combiner. The first optical path 136A exits the output coupling region of the waveguide combiner. While FIG. 1 depicts the optical device 102 as a waveguide combiner, the optical device 102 may be any suitable optical device, such as a metasurface. In an embodiment in which the optical device 102 is a metasurface, the first optical path 136A enters the first surface 104 of the metasurface. The first optical path 136A is directed toward a center point 144 of the metasurface. The first optical path 136A passes through the metasurface and exits from the center point 144 of the metasurface.

[0020] First optical path 136A is operable to be incident on mirror 116. Mirror 116 is disposed adjacent second surface 106 of optical device 102 along first optical path 136A. Mirror 116 is operable to direct first optical path 136A to first lens 126. First lens 126 is operable to direct first optical path 136A to third beam splitter 118. In one embodiment, which may be combined with other embodiments described herein, first lens 126 may be disposed between second surface 106 and mirror 116. In another embodiment, which may be combined with other embodiments described herein, first lens 126 may be disposed between mirror 116 and third beam splitter 118, as shown in FIG. 1 . First lens 126 is a relay lens. In yet another embodiment, which may be combined with other embodiments described herein, the auxiliary lens 142 is positioned between the optical device 102 and the mirror 116. The auxiliary lens 142 is a relay lens.

[0021] The second optical path 136B enters the second beam splitter 114. In one embodiment, which may be combined with other embodiments described herein, one or both of a second lens 132 and a pinhole 134 are disposed in the second optical path 136B between the first beam splitter 112 and the second beam splitter 114. The second optical path 136B may pass through one or both of the second lens 132 and the pinhole 134. The second lens 132 is a relay lens. The pinhole 134 is operable to act as a low-pass filter for the second optical path 136B. The second beam splitter 114 is disposed adjacent to the phase modulator 120. The second beam splitter 114 is operable to direct the second optical path 136B to the phase modulator 120.

[0022] The phase modulator 120 is operable to change the phase of the second light path 136B. In a first configuration of the phase modulator 120, the phase modulator 120 is a spatial light modulator. In a second configuration of the phase modulator 120, the phase modulator 120 is a piezoelectrically driven mirror. In a third configuration of the phase modulator 120, the phase modulator 120 is a tilting mirror. The phase modulator 120 changes the phase of the second light path 136B. The second light path 136B is directed to the third beam splitter 118. The phase modulator 120 generates one or more phase-modulated images of the second light path 136B. In embodiments having the first or second configuration, one or more phase-delayed images can be created. In embodiments having the third configuration, one or more linear phase-delayed images can be created.

[0023] In the first embodiment, a third lens 122A and a fourth lens 122B are disposed along the second optical path 136B. The third lens 122A is adjacent to the phase modulator 120. The fourth lens 122B is adjacent to the detector 128. In the second embodiment, a fifth lens 124 is disposed along the second optical path 136B. To direct the second optical path 136B into the metrology tool 100, the first embodiment utilizes the third lens 122A and the fourth lens 122B, and the second embodiment utilizes the fifth lens 124. The third lens 122A, the fourth lens 122B, and the fifth lens 124 are relay lenses.

[0024] The third beam splitter 118 is operable to direct the first optical path 136A and the second optical path 136B toward the detector 128. The third beam splitter 118 superimposes the first optical path 136A and the second optical path 136B into a superimposed optical path. The detector 128 is operable to obtain intensity measurements of the superimposed optical path. The detector 128 is operable to utilize the intensity measurements to reconstruct the full-field optical field at a reference point 138. The reference point 138 is located directly adjacent to the second surface 106. The reference point 138 is located adjacent to a surface of the optical device 102 where the first optical path 136A exits the optical device. Metrology metrics of the optical device 102 are derived from the full-field optical field during post-processing. The metrology tool 100 is in communication with a controller 140 operable to control operation of the metrology tool 100.

[0025] 2 is a schematic cross-sectional view of a metrology tool 200. The metrology tool 200 is operable to hold a substrate 108. The substrate 108 includes at least one optical device 102 disposed thereon.

[0026] It should be understood that the at least one optical device 102 described herein is an exemplary optical device, and that other optical devices may be used with or modified to achieve aspects of the present disclosure. In one embodiment that may be combined with other embodiments described herein, the optical device 102 is a waveguide combiner. Waveguide combiners may be utilized for virtual reality, augmented reality, or mixed reality. In an embodiment in which the optical device 102 is a waveguide combiner, an input coupling region may be disposed on a first surface 104 of the optical device 102. An output coupling region may be disposed on a second surface 106 of the optical device 102. The second surface 106 is on a surface opposite the first surface 104. In another embodiment that may be combined with other embodiments described herein, the waveguide combiner includes an input coupling region and an output coupling region on the same surface, for example, on one of the first surface 104 or the second surface 106. In yet another embodiment, which may be combined with other embodiments described herein, the optical device 102 is a planar optical device, such as a metasurface.

[0027] The metrology tool 200 is operable to measure the full-field optical field of at least one optical device 102. The full-field optical field of the optical device 102 provides a complete characterization of the optical device 102. The full-field optical field includes the amplitude and phase of the light rays. The full-field optical field provides direct information of the optical device 102 by measuring the full-field optical field in parallel. Metrology metrics can be obtained from the full-field optical field to ensure the design of the optical device 102 is verified and optical device metrology metrics are monitored. Embodiments of the metrology tool 200 described herein provide the ability to obtain multiple metrology metrics with increased throughput. The metrology metrics include one or more of an angular uniformity metric, a contrast metric, an efficiency metric, a color uniformity metric, a modulation transfer function (MTF) metric, a field of view (FOV) metric, a ghost image metric, or an eyebox metric for a waveguide combiner, and an efficiency metric, a point spread function (PSF) metric, a modulation transfer MTF metric, or a phase error metric for a metasurface.

[0028] The metrology tool 200 includes a light engine 210, a first beam splitter 212, a second beam splitter 218, a mirror 216, a tilt mirror 220, a first lens 222A, a second lens 222B, an auxiliary lens 242, and a detector 228. The light engine 210 is operable to project a light beam onto the first beam splitter 212. In one embodiment, which may be combined with other embodiments described herein, the light engine 210 is a light emitting diode (LED) or a laser. In another embodiment, which may be combined with other embodiments described herein, the light engine 210 includes a display module. The display module is operable to project a pattern onto the optical device 102. The display module may include a micro LED module, a liquid crystal on silicon (LCOS) module, a digital light processing (DLP) module, or a laser projection module.

[0029] The first beam splitter 212 splits the light beam into a first optical path 236A and a second optical path 236B. The optical device 102 is disposed in the first optical path 236A. The optical device 102 may be any suitable optical device, such as a waveguide combiner or a metasurface. The first optical path 236A is directed toward the optical device 102 to be measured. The first optical path 236A is incident on the first surface 104 of the optical device 102. In some embodiments, which may be combined with other embodiments described herein, the first modulation module 213 and the second modulation module 214 are disposed adjacent to the first surface 104 of the optical device 102. The first modulation module 213 and the second modulation module 214 are disposed on either side of the optical device 102. The first modulation module 213 and the second modulation module 214 are operable to change the phase, amplitude, or angle of incidence of the first optical path 236A.

[0030] In an embodiment in which the optical device 102 is a metasurface, as shown in FIG. 2, a first light path 236A is incident on the first surface 104 of the metasurface. The first light path 236A is directed toward the center point 144 of the metasurface. The first light path 236A passes through the metasurface and exits from the center point 144 of the metasurface. Although FIG. 2 depicts the optical device 102 as a metasurface, the optical device 102 may be any suitable optical device, such as a waveguide combiner.

[0031] 1, in an embodiment in which the optical device 102 is a waveguide combiner, the first optical path 236A enters the input coupling region. The first optical path 236A passes through the waveguide combiner. The first optical path 236A exits the output coupling region of the waveguide combiner.

[0032] The first optical path 236A is operable to be incident on the mirror 216. The auxiliary lens 242 is disposed between the optical device 102 and the mirror 216. The auxiliary lens 242 is a relay lens. The mirror 216 is disposed along the first optical path 236A adjacent to the second surface 106 of the optical device 102. The mirror 216 is operable to direct the first optical path 236A to the second beam splitter 218.

[0033] The second optical path 236B is incident on the tilt mirror 220. The tilt mirror 220 is operable to change the phase of the second optical path 236B. The tilt mirror 220 changes the phase of the second optical path 236B. The second optical path 236B is directed to the second beam splitter 218. The tilt mirror 220 generates one or more linear phase-delayed images of the second optical path 236B. A first lens 222A and a second lens 222B are disposed along the second optical path 236B. The first lens 222A is adjacent to the tilt mirror 220. The second lens 222B is adjacent to the detector 228. The first lens 222A and the second lens 222B are relay lenses.

[0034] The second beam splitter 218 is operable to direct the first optical path 236A and the second optical path 236B toward the detector 228. The second beam splitter 218 superimposes the first optical path 236A and the second optical path 236B into a superimposed optical path. The detector 228 is operable to obtain intensity measurements of the superimposed optical path. The detector 228 is operable to utilize the intensity measurements to reconstruct the full-field optical field at a reference point 238. The reference point 238 is located directly adjacent to the second surface 106. The reference point 238 is located adjacent to a surface of the optical device 102 where the first optical path 236A exits the optical device 102. Metrology metrics of the optical device 102 are derived from the full-field optical field during post-processing. The metrology tool 200 is in communication with a controller 140 operable to control operation of the metrology tool 200.

[0035] 3 is a flow diagram of a method 300 for determining a full-field optical field of at least one optical device 102. The at least one optical device 102 is disposed on a substrate 108 disposed in a metrology tool 100. For ease of explanation, the method 300 will be described with respect to the metrology tool 100 as shown in FIG. 1. The controller 140 of the metrology tool 100 is operable to facilitate operation of the method 300. The method 300 is operable to be implemented in conjunction with the metrology tool 200.

[0036] A light beam is projected in operation 301. The light beam is projected from light engine 110 to first beam splitter 112. First beam splitter 112 splits the light beam into first light path 136A and second light path 136B.

[0037] In operation 302, a first light path 136A is projected to enter the optical device 102. In embodiments where the optical device 102 is a waveguide combiner, the first light path 136A enters an input coupling region corresponding to the first surface 104. The first light path 136A passes through the optical device 102. The first light path 136A exits an output coupling region of the optical device 102. The waveguide combiner is positioned such that the first light path 136A is operable to enter the input coupling region of the waveguide combiner. In embodiments where the optical device 102 is a metasurface, the first light path 136A enters the first surface 104 of the metasurface. The first light path 136A is directed toward a center point 144 of the metasurface. The first light path 136A passes through the metasurface and exits through the second surface 106 via the center point 144 of the metasurface. The metasurface is positioned such that a first light path 136A is operable to be incident on the metasurface at a center point 144. The first light path 136A is directed towards the detector 128.

[0038] In operation 303, one or more phase-modulated images are created. In one embodiment, which may be combined with other embodiments described herein, the one or more phase-modulated images are phase-delayed images. The second light path 136B is incident on the phase modulator 120 to create one or more phase-delayed images. In the first and second configurations of the phase modulator 120, the phase modulator 120 is a spatial light modulator or a piezoelectrically driven mirror. When the phase modulator 120 is in the first or second configuration, the phase modulator 120 is operable to generate one or more phase delays of the second light path 136B. For example, four phase-delayed images of the second light path 136B (i.e., 0.5π, π, 1.5π, and 2π) are provided to and recorded by the detector 128. Each phase-delayed image changes the intensity of the first light path 136A and the second light path 136B on the detector 128. Additionally, three or more phase delayed images reduce the effect of noise on the detector 128. In a third configuration of the phase modulator 120, the phase modulator 120 is a tilting mirror.

[0039] In another embodiment, which may be combined with other embodiments described herein, the one or more phase-modulated images are linear phase-delayed images. When the phase modulator 120 is in the third configuration, a tilted mirror is utilized. The tilted mirror forms one or more linear phase-delayed images with a linear phase change. The tilted mirror is angled at a predefined angle so that one or more linear phase-delayed images can be formed without aliasing. The linear phase-delayed image of the second optical path 136B is provided to the detector 128.

[0040] In operation 304, the first optical path 136A and the second optical path 136B are superimposed. The first optical path 136A and the second optical path 136B are superimposed by the third beam splitter 118. The first optical path 136A and the second optical path 136B are superimposed to form a superimposed optical path. The superimposed optical path is incident on the detector 128. The first lens 126 relays the first optical path 136A to the detector 128. In some embodiments, the fourth lens 122B also relays the reference field to the detector 128. The second lens 132 relays the optical field of one or more phase-delayed images from the phase modulator 120 to the detector 128. In some embodiments, the third lens 122A or the fifth lens 124 also relays the optical field of one or more phase-delayed images to the detector 128.

[0041] In operation 305, the full-field optical field of the optical device 102 at reference point 138 is determined. Reference point 138 is located directly adjacent to second surface 106. In one embodiment, which may be combined with other embodiments described herein, reference point 138 is located at the output coupling region of optical device 102. The full-field optical field provides a complete characterization of the optical device 102. The full-field optical field at reference point 138 includes determining the amplitude and phase at reference point 138. In one embodiment, which may be combined with other embodiments described herein, the phase profile is directly compared to the design of optical device 102, thus providing feedback to the manufacturing process. Detector 128 records intensity measurements of the superimposed light paths to determine the amplitude and phase. When phase modulator 120 is in the first configuration or the second configuration, a first equation may be utilized to determine the intensity measurement I(x, y; Φ) of the superimposed light beam. I(x,y;Φ)=I1(x,y)+I2(x,y)cos(Ψ(x,y)+Φ) where I1 is the intensity measurement of the first light path 136A, I2 is the intensity measurement of the second light path 136B, Φ is the phase of one or more phase-delayed images provided by the phase modulator 120, and Ψ is the phase of the first light path 136A at the reference point 138. I1 and I2 contain amplitude information at the reference point 138. By varying the phase Φ of the phase-delayed images with the phase modulator 120, multiple different images are utilized to solve for the amplitude and phase Ψ at the reference point 138. For example, a Fourier transform of (x, Φ) will reconstruct the amplitude and phase Ψ at the reference point 138. The amplitude and phase Ψ at the reference point 138 correspond to the full-field optical field.

[0042] When the phase modulator 120 is in the third configuration, the second equation is expressed as the intensity measurement I(x,y;Φ x,y ) can be used to determine I(x,y;Φ)=I1(x,y)+I2(x,y)cos(Ψ(x,y)+Φ x,y ) where I1 is the intensity measurement of the first light path 136A, I2 is the intensity measurement of the second light path 136B, Φ is the phase of the linear phase-delayed image provided by the phase modulator 120, and Ψ is the phase of the first light path 136A at the reference point 138. I1 and I2 contain amplitude information at the reference point 138. The tilting mirror brings the phase-delayed image Φ up to a high frequency region. That image is used to solve for the amplitude and phase Ψ at the reference point 138. For example, a Fourier transform of (x, Φ) will reconstruct the amplitude and phase Ψ at the reference point 138. The amplitude and phase Ψ at the reference point 138 correspond to the full-field optical field.

[0043] In one embodiment, which may be combined with other embodiments described herein, when the optical device 102 is a waveguide combiner, the full-field optical field at the reference point 138 may be inspected to determine correlation with the image quality of the waveguide combiner. Additionally, full-field optics may be utilized to monitor the uniformity of the optical device structure across the waveguide combiner. To monitor the uniformity of the optical device structure across the waveguide combiner, including the critical dimensions, depth, trench fill, overcoating, etc. of the optical device structure, variations between each waveguide combiner are collected and organized into a library of empirical data.

[0044] In operation 306, metrology metrics are determined. The full-field optical field at reference point 138 is determined in operation 305. Metrology metrics of optical device 102 are derived from the full-field optical field during post-processing. The metrology metrics can be used to predict optical device performance in the far field. The metrology metrics can be used to validate optical device design and monitor optical device performance. In embodiments where optical device 102 is a waveguide combiner, the metrology metrics include, but are not limited to, one or more of an angular uniformity metric, a contrast metric, an efficiency metric, a color uniformity metric, a modulation transfer function (MTF) metric, a field of view (FOV) metric, a ghost image metric, or an eyebox metric. In embodiments where optical device 102 is a metasurface, the metrology metrics include, but are not limited to, one or more of an efficiency metric, a point spread function (PSF) metric, an MTF metric, or a phase error metric. The ability to derive any desired metrology metric from a single physical measurement improves throughput, reduces storage and bandwidth requirements, and reduces costs associated with analyzing optical device 102.

[0045] In summary, provided herein are metrology tools and methods for acquiring a full-field optical field of an optical device to determine multiple metrology metrics of the optical device. The metrology tool is utilized to split a light beam into a first light path and a second light path. The first light path travels through at least one optical device, such as a metasurface or a waveguide combiner, and is directed to a detector. The second light path is directed to a phase modulator. One or more phase-modulated images of the second light path are captured by the detector. The first light path and the second light path are combined into a combined light beam and sent to the detector. The detector measures the intensity of the combined light beam. First and second equations are utilized in combination with the intensity measurements to determine an amplitude and phase Ψ at a reference point directly adjacent the second surface of the at least one optical device. The amplitude and phase Ψ correspond to the full-field optical field of the optical device. Metrology metrics can be derived from the full-field optical field. The methods described herein improve throughput, reduce storage and bandwidth requirements, and reduce costs associated with analyzing optical devices.

[0046] While the foregoing is directed to embodiments of the present disclosure, other embodiments of the disclosure may be devised without departing from the basic scope thereof, which scope is determined by the following claims.

Claims

1. A measurement tool comprising: a light engine operable to project a light beam; a first beam splitter disposed in a path of the light beam, the first beam splitter operable to split the light beam into a first optical path and a second optical path, the first optical path operable to be incident on an optical device; a phase modulator disposed in the second optical path; a second beam splitter disposed in the first optical path and the second optical path, the second beam splitter operable to overlap the first optical path and the second optical path to form a overlapped optical path; a detector disposed in the superimposed light path, the detector operable to record intensity measurements of the superimposed light path; A controller comprising instructions that, when executed, cause a plurality of operations to be performed, The plurality of operations include: and a controller that determines a full-field optical field of the optical device at a reference point located adjacent a second surface of the optical device where the first optical path exits the optical device, the full-field optical field being determined by performing a Fourier transform on the intensity measurements to reconstruct the amplitude and phase of the first optical path at the reference point.

2. 2. The metrology tool of claim 1, wherein the optical device is a waveguide combiner, the waveguide combiner being positioned such that the first optical path is operable to enter an input coupling region of the waveguide combiner.

3. The metrology tool of claim 1 , wherein the optical device is a metasurface, the metasurface being positioned such that the first light path is operable to be incident on a center point of the metasurface.

4. The metrology tool of claim 1 , wherein the phase modulator is one of a spatial light modulator, a piezoelectrically actuated mirror, or a tilting mirror.

5. The metrology tool of claim 1 , wherein the light engine projects a laser.

6. The metrology tool of claim 1 , wherein the phase modulator is operable to vary the phase of the second optical path.

7. a first lens disposed in the first optical path, the first lens operable to relay the first optical path; a second lens disposed in the second optical path, the second lens operable to relay the second optical path; and a third lens disposed in the second optical path, the third lens operable to relay the second optical path; and a fourth lens disposed in the second optical path, the fourth lens operable to relay the second optical path; and The metrology tool of claim 1 further comprising:

8. The metrology tool of claim 1 , further comprising a linear polarizer operable to polarize the light beam.

9. The metrology tool of claim 1 , further comprising an auxiliary lens disposed in the first optical path, the auxiliary lens operable to relay the first optical path.

10. A measurement tool comprising: a light engine operable to project a light beam; a first beam splitter disposed in a path of the light beam, the first beam splitter operable to split the light beam into a first optical path and a second optical path, the first optical path operable to be incident on an optical device; a modulation module disposed in the first optical path, the modulation module operable to change a phase, an amplitude, or an angle of incidence of the first optical path; a tilt mirror disposed in the second optical path; and a second beam splitter disposed in the first optical path and the second optical path, the second beam splitter operable to overlap the first optical path and the second optical path to form a overlapped optical path; a detector disposed in the superimposed light path, the detector operable to record intensity measurements of the superimposed light path; A controller comprising instructions that, when executed, cause a plurality of operations to be performed, The plurality of operations include: determining a full-field optical field of the optical device at a reference point located adjacent a second surface of the optical device where the first optical path exits the optical device, the full-field optical field being determined by performing a Fourier transform on the intensity measurements to reconstruct the amplitude and phase of the first optical path at the reference point; and A measurement tool comprising:

11. 11. The metrology tool of claim 10, wherein the optical device is a waveguide combiner, the waveguide combiner being positioned such that the first optical path is operable to enter an input coupling region of the waveguide combiner.

12. The metrology tool of claim 10 , wherein the optical device is a metasurface, the metasurface being positioned such that the first light path is operable to be incident on a center point of the metasurface.

13. a first lens disposed in the second optical path, the first lens operable to relay the second optical path; a second lens disposed in the second optical path, the second lens operable to relay the superimposed optical path; an auxiliary lens disposed in the first optical path, the auxiliary lens operable to relay the first optical path; and The metrology tool of claim 10 further comprising:

14. projecting the light beam onto a first beam splitter, the first beam splitter splitting the light beam into a first optical path and a second optical path; projecting the first light path onto an optical device, the first light path traveling through the optical device, the optical device being a metasurface or a waveguide combiner; projecting the second light path onto a phase modulator, the phase modulator operable to generate one or more phase-delayed images of the second light path; superimposing the first optical path and the second optical path by a second beam splitter to form a superimposed optical path; directing the superimposed light path to a detector, the detector operable to record intensity measurements of the first light path and the second light path; determining a full-field optical field of the optical device at a reference point located adjacent a surface of the optical device where the first optical path exits the optical device, the full-field optical field being determined by performing a Fourier transform on the intensity measurements to reconstruct the amplitude and phase of the first optical path at the reference point; A method comprising:

15. The method of claim 14 , further comprising determining a metrology metric, wherein the metrology metric is determined from the full-field optical field during post-processing.

16. 16. The method of claim 15, wherein the measurement metrics include one or more of an angular uniformity metric, a contrast metric, an efficiency metric, a color uniformity metric, a modulation transfer function (MTF) metric, a field of view (FOV) metric, a ghost image metric, or an eyebox metric.

17. The method of claim 14 , wherein the full-field optical field is determined in the high frequency domain.

18. The method of claim 14 , wherein each of the one or more phase-delayed images modifies the intensity measurements of the superimposed light paths on the detector.

19. 15. The method of claim 14, further comprising: positioning the optical device such that the optical device is the waveguide combiner, the first light path being operable to enter an input coupling region of the optical device.

20. 15. The method of claim 14, further comprising: positioning the optical device such that the optical device is the metasurface and the first light path is incident on a center point of the optical device.

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