Eyepiece for head-mounted display and method of manufacturing the same

Abstract

A method includes providing a wafer including a first surface grating extending over a first region of a surface of the wafer and a second surface grating extending over a second region of the surface of the wafer, de-functionalizing a portion of the surface grating in at least one of the first surface grating region and the second surface grating region, and singulating an eyepiece from the wafer, the eyepiece including a portion of the first surface grating region and a portion of the second surface grating region. The first surface grating in the eyepiece corresponds to an input-coupling grating for a head-mounted display, and the second surface grating corresponds to a pupil expander grating for the head-mounted display.

Description

[0001] CLAIM OF PRIORITY

[0002] This application claims the benefit of priority under 35 USC § 119(e) to U.S. Patent Application Serial No. 63 / 044,124, filed June 25, 2020, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to head-mounted displays, and more particularly to eyepieces for head-mounted displays and methods of manufacturing eyepieces. BACKGROUND

[0004] Optical imaging systems such as wearable display systems (e.g., wearable display headsets) can include one or more eyepieces that present a projected image to a user. The eyepieces can be constructed using thin layers of one or more high-refractive materials. As an example, the eyepieces can be composed of one or more layers of high-refractive glass, silicon, metal, or polymer substrates.

[0005] Multiple eyepieces can be used in conjunction to project simulated three-dimensional images. For example, multiple eyepieces each having a different pattern can be stacked on top of one another, and each eyepiece can project a volumetric image of a different depth layer. Thus, the eyepieces can collectively present a volumetric image to a user in three dimensions. This is useful, for example, in presenting a “virtual reality” environment to a user.

[0006] In some cases, the eyepieces include thin layers of material that include surface gratings formed on their respective surfaces. These layers can be formed by casting the material and molding the surface gratings during a casting process. The gratings for multiple eyepieces can be cast in a single thin film, and individual eyepieces are singulated from the cast film. SUMMARY

[0007] In certain implementations, eyepieces used in wearable display headsets use two surface gratings: one to inject projected light into a waveguide (e.g., an input-coupling grating), and another to increase the size of the display exit pupil (e.g., a pupil expander grating). These eyepieces are typically singulated (e.g., cut) from a master polymer wafer in which the surface gratings are molded. These wafers are typically cast with the grating arrangement set by the mold, establishing the area covered by both surface gratings, the shape of each grating, the pitch and orientation, and the spacing between the two grating areas.

[0008] Eyepiece surface grating regions can be cast and oriented such that a wide range of distances between a user’s pupils can be accommodated. This accommodation is achieved through casting of a host polymer layer that includes a super-sized region for an in-coupling grating region and a pupil expander grating region, or both. This super-sized region is then partially defunctionalized to reduce the area of the grating, such that eyepieces with accommodated different pupil distances can be accommodated using a single wafer mold.

[0009] Various aspects of the present invention are summarized as follows.

[0010] Generally, in a first aspect, the invention features a method comprising: providing a wafer comprising a first surface grating extending over a first region of a surface of the wafer and a second surface grating extending over a second region of the surface of the wafer; defunctionalizing a portion of the surface grating in at least one of the first surface grating region and the second surface grating region; and singulating an eyepiece from the wafer, the eyepiece comprising a portion of the first surface grating region and a portion of the second surface grating region. The first surface grating in the eyepiece corresponds to an in-coupling grating for a head-mounted display, and the second surface grating corresponds to a pupil expander grating for the head-mounted display.

[0011] Embodiments of the method can include one or more of the following features. Defunctionalizing the portion of the first surface grating or the second surface grating can include planarizing the portion of the corresponding surface grating. Planarizing the portion of the first surface grating or the second surface grating can include casting a material over the corresponding portion of the surface grating. The material that is cast can be the same material as the material that forms the surface grating.

[0012] In some embodiments, the method can further include depositing a reflective material on a portion of the first surface grating. The reflective material can be a metal.

[0013] The height of the defunctionalized portion of the first surface grating region or the second surface grating region above the surface can be greater than the height of the first surface grating features or the second surface grating features. For the defunctionalized portion of the first surface grating region or the second surface grating region, the height of the defunctionalized portion can be no more than 100 nm greater than the height of the corresponding surface grating features.

[0014] Providing the wafer can include: imprinting the first grating and the second grating onto the surface of the wafer. Alternatively, providing the wafer can include: casting a wafer having the first grating and the second grating.

[0015] The second region can have a minimum lateral dimension greater than 30 mm.

[0016] The pupil expander grating can have a maximum lateral dimension of 30 mm or less.

[0017] The input-coupling grating can have a maximum lateral dimension of 5 mm or less.

[0018] In some embodiments, the method can further include assembling the eyepiece in a head-mounted display.

[0019] In a second aspect, the invention features an article including: a planar waveguide formed of a polymeric material, the planar waveguide including a first surface including: a first surface grating; a second surface grating spaced apart from the first surface grating; and a smooth portion between the first surface grating and the second surface grating. The smooth portion includes a first region at a first surface height, the first grating and the second grating each extending above the first surface height, and the smooth portion includes a second region adjacent to the first surface grating or the second surface grating, the second region extending to a height higher than the adjacent surface grating.

[0020] Embodiments of the article can include one or more of the following features. The article can further include a reflective layer supported by the first surface grating. The first surface grating and the reflective layer can be configured to couple incident light into the planar waveguide to propagate toward the second surface grating.

[0021] The second surface grating can be configured to out-couple light guided by the waveguide from the waveguide.

[0022] The second region can extend 100 nm or less above the adjacent surface grating.

[0023] The first surface grating can have a maximum lateral dimension of 5 mm or less, and the second surface grating can have a maximum lateral dimension of 30 mm or less.

[0024] The first grating and the second grating can be spaced apart by 10 mm or more.

[0025] In a third aspect, the invention further features a head-mounted display including an eyepiece, the eyepiece including an article of the invention. The display can be a virtual retinal display.

[0026] Among other advantages, these implementations can provide manufacturing efficiency by allowing the use of a single mold geometry to manufacture eyepieces for different pupil distances.

[0027] Other advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1A FIG. 1 is a schematic diagram illustrating a head-mounted display and alignment of the display’s eyepiece with a user’s eye. 1B

[0029] Figure 2 FIG. 4 is a schematic diagram illustrating an example of a master polymer wafer having multiple surface grating regions and example parting lines for multiple lenses.

[0030] Figure 3 FIG. 5 is a second schematic diagram illustrating an example of a master polymer wafer having multiple surface grating regions and example parting lines for multiple lenses.

[0031] Figure 4A FIG. 6 is a schematic diagram illustrating an example method for de-functionalizing surface grating regions corresponding to in-coupling gratings. 4B

[0032] Figure 5A FIG. 7 is a schematic diagram illustrating an example method for de-functionalizing surface grating regions corresponding to out-coupling expanders. 5B

[0033] FIG. 8 is a schematic diagram illustrating steps in an example method for de- functionalizing surface grating regions using polymer droplets. Figures 6A-6E

[0034] FIG. 9 is a schematic diagram illustrating steps in an example method for de- functionalizing surface grating regions using a heated stage and a stamp having voids. Figures 7A-7C

[0035] FIG. 10 is a schematic diagram illustrating steps in an example method for de- functionalizing surface grating regions using a heated stage and a stamp having embedded gratings. Figure 8A

[0036] FIG. 11 is a flowchart illustrating an example method for parting multiple eyepieces from a master polymer wafer. Figure 9 In the drawings, like reference numerals indicate like elements.

[0037] DETAILED DESCRIPTION

[0038] Reference Figure 1A ​​​The eyepiece 100 of the head-mounted display system directs light from the projector 120 to the user’s eye 110. The projector 120 and the eyepiece 100 are positioned relative to each other and to the user’s eye 110 by a frame or housing (not shown). The projector 120 is positioned to the side of the user’s temple and directs light to an end of the eyepiece 100 that extends past the user’s temple. The eyepiece 100 includes a planar waveguide 140, an input-coupling grating (ICG) 130, and an out-coupling element (OCE) 150.

[0039] The ICG 130 is a surface grating positioned to receive light from the projector 120 and facilitate coupling of light from the projector 120 into the eyepiece 100. The ICG 130 is located at or near an edge of the eyepiece 100 closest to the projector 120. The ICG 130 directs light from the projector 120 into a guided mode in the planar waveguide substrate 140 of the eyepiece 100.

[0040] The ICG 130 can have any size sufficient to receive light from the projector. In some embodiments, the lateral dimension can be in a range of 0.5 mm to 5.0 mm (e.g., 1.0 mm or more, 1.5 mm or more, 2.0 mm or more, 2.5 mm or more, such as 4.0 mm or less, 3.0 mm or less).

[0041] The planar waveguide substrate 140 directs the coupled-in light along the eyepiece 100 by total internal reflection at its surfaces to the out-coupling element (OCE) 150. The OCE 150 is a second surface grating configured to extract light from the planar waveguide substrate 140 and redirect it toward the user’s eye 110. The OCE 150 can include an exit pupil expander (EPE) or an orthogonal pupil expander (OPE) or both. Ideally, the OCE 150 is located in front of the user’s eye 110 so that light can be delivered from the projector to an eyebox 160, as described below. The OCE 150 can also have a lateral dimension 151 to accommodate a range of lateral positions of the eyebox 160. For example, a non-limiting range of the lateral dimension 151 of the OCE 150 can be 30 mm or less (e.g., 25 mm or less, 20 mm or less, 15 mm or less).

[0042] The eyebox 160 is considered to be an area in which the pupil 112 of the user can be positioned to receive light output from the OCE 150. The eyebox 160 can include an eye relief 162 range from the planar waveguide substrate, including but not limited to 5 mm to 25 mm (e.g., 5 to 10 mm, 5 to 15 mm, 5 to 20 mm, 10 to 25 mm, 15 to 25 mm, 20 to 25 mm).

[0043] Referring toFigure 1B When placed in a head-mounted display system, a pair of eyepieces 100 are positioned such that the lateral eyepiece separation 180 accommodates the center-to-center distance between the user’s pupils 112, referred to as the interpupillary distance (IPD) 190. Generally, the IPD 190 can vary across a group of individuals. On average, the IPD of an adult human is approximately 62 mm, but can vary from approximately 50 mm to approximately 80 mm.

[0044] Generally, the eyepieces 100 can be manufactured to have a single center-to-center distance 170 between the ICG 130 and the OCE 150, but have an oversized OCE 150 (e.g., having a lateral dimension of 36 mm or greater) such that the eyepieces can accommodate a range of IPD 190.

[0045] In some embodiments, multiple eyepieces 100 can be singulated from a single master polymer wafer. The master polymer wafer can include a first surface grating extending over a first region of a surface of the wafer and a second surface grating extending over a second region of the surface of the wafer. The first and second surface grating regions can be cast into the master polymer wafer at the time of molding. Alternatively, the first and second surface grating regions can be imprinted into the master polymer wafer after molding. The eyepieces 100 can be singulated from the master polymer wafer such that they include the OCE surface grating region, the ICG surface grating region, and a smooth portion between the two surface grating regions.

[0046] The methods described below can be used to produce eyepieces with one or more different OCE 150 and ICG 130 surface grating regions in one or more different configurations and orientations using a single master polymer wafer mold. In this way, multiple eyepieces can be singulated from a master polymer wafer, each with a different surface grating center-to-center distance.

[0047] For example, in some implementations, the master polymer wafer can include oversized surface grating regions that allow for eyepiece singulation over a range of center-to-center distances. Referring to Figure 2 , an example master polymer wafer 210 includes surface grating regions from which three different eyepieces can be singulated. The master polymer wafer 210 is cast to have three surface grating regions 220 corresponding to three OCEs. In addition, the master polymer wafer 210 has three oversized surface grating regions 222 corresponding to three ICGs 230. The surface grating regions 220 and the oversized surface grating regions 222 are spaced apart by smooth portions 240. Generally, the surface grating regions 220 and the oversized surface grating regions 222 are imprinted on a surface of the master polymer wafer 210.

[0048] Because the surface grating region 222 is oversized (i.e., larger than the area required for the ICG 230), the eyepiece can be segmented to include different portions of the oversized grating region, and the eyepiece still provides a portion of the grating region 222 at the proper location of the ICG 230 relative to the edge of the eyepiece. This is shown in Figure 2 FIG. 11, where the eyepieces 200a, 200b, and 200c are segmented to provide three different spacings between the OCEs of the eyepiece. In particular, for the eyepiece 200a, the eyepiece is segmented to include a relatively large portion of the grating region 222, resulting in a larger spacing 170a between the ICG 230 and the center of the grating region 220. For the eyepiece 200b, the segmentation includes a middle portion of the grating region 222, providing an intermediate spacing 170b between the ICG and the center of the grating region 220. For the eyepiece 200c, the segmentation includes a small region of the grating region 222, corresponding to a small spacing 17-c between the ICG and the center of the grating region 220. Note that in each case, the ICG 230 is at the same location relative to the edge of the eyepiece. As will be described in more detail below, the portions of the grating region 222 outside of the ICG 230 can be de-functionalized, either before or after segmentation, leaving only the grating in the region corresponding to the ICG.

[0049] In general, the sizes of the grating regions 220 and 222, and the spacing 240 between them, can be varied as appropriate depending on the size and shape of the eyepiece, ICG, and OCE. In some embodiments, the spacing 240 corresponding to the smooth portion can be 10 mm or more (e.g., 15 mm or more, 20 mm or more). The diameter of the first surface grating region 220 corresponding to the OCE can be in the range of 20 mm to 40 mm (e.g., 22 mm or more, 25 mm or more, 28 mm or more, e.g., 35 mm or less, 30 mm or less).

[0050] The surface grating region 222 should be large enough to allow the ICG to be provided at multiple different locations. Thus, the region 222 can have at least one dimension (e.g., diameter) that is at least twice (e.g., 3 times or more, 4 times or more, 5 times or more) the largest dimension of the ICG. In some embodiments, the diameter of the surface grating region 222 is in the range of 5 mm to 50 mm (e.g., 8 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, e.g., 40 mm or less, 30 mm or less).

[0051] The host polymer wafer 210 can be made of any polymer material suitable for producing a lens with an appropriate surface grating.

[0052] While Figure 2The surface grating regions 220 and 222 are depicted as circular, but more generally, the surface grating regions 220 and 222 can be any shape (e.g., circular, square, triangular). Moreover, while the surface grating regions 220 and 222 are depicted as being spaced apart from each other, in some implementations, the surface grating regions 220 and 222 can be contiguous with each other. Figure 2 Three eyepieces are shown being singulated from the polymer wafer 210, but the size of the wafer can be set to provide fewer or more than three eyepieces (e.g., two, four, five, six, or more).

[0053] After singulating the eyepieces 200 from the master polymer wafer 210, the eyepieces 200 can then be further processed as needed and ultimately assembled into a head-mounted display.

[0054] While the above examples feature a super-sized grating region for the ICG 130, other implementations are possible. For example, Figure 3 A second example of a master polymer wafer 310 having multiple surface grating regions is shown. Here, the master polymer wafer 310 is cast to have a single super-sized surface grating region 324 spaced apart by a smooth region 340 and three additional surface gratings corresponding to ICGs 330.

[0055] In this example, the eyepieces 300a-300c are singulated from the master polymer wafer 310 to provide OCEs 350a, 350b, and 350c, respectively, each having a different size and each spaced apart from the ICGs by a different amount (370a, 370b, and 370c, respectively). The size and shape of the super-sized surface grating region 324 can be set to provide a desired number of eyepieces with OCEs at desired locations relative to the ICGs. The region can have a lateral dimension of 100 mm or more (e.g., 350 mm or more, 200 mm or more). In some embodiments, the grating region 324 can span the diameter of the wafer 310.

[0056] The super-sized surface grating region 324 is de-functionalized to yield three OCEs 350 having different lateral dimensions. Thus, the center-to-center distance 370 between the ICGs 330 and the OCEs 350 can be controlled. Figure 3 Three example center-to-center distances 370a, 370b, and 370c are shown, which can correspond to the example short IPD 190, medium IPD 190, and long IPD 190, respectively.

[0057] It should be noted that while the foregoing two examples describe forming a super-sized grating for either the ICG or the OCE, in some implementations, a super-sized grating can be formed for both.

[0058] Turning now to the process of grating de-functionalization, this typically involves planarizing the surface grating structure such that the portion of the grating area that is de-functionalized no longer functions as a grating. Figure 4A and 4B An example process of metallization and de-functionalization of a super-sized surface area 422 corresponding to the ICG 130 shown in Figure 1A

[0059] Figure 4A A cross-sectional view of a master polymer wafer 410 including a substrate portion 412 having a surface grating area 420 corresponding to an OCE and a super-sized surface grating area 422 for providing an ICG 130 is shown.

[0060] As Figure 4B shown, prior to de-functionalizing a portion of the surface grating area 422, a reflective material 426 (e.g., metal) is deposited in a portion 423 of the grating area 422 corresponding to the ICG.

[0061] A polymer layer 440 is then cast over the remaining grating area 422, planarizing the entire area. Typically, the polymer used to planarize the grating area 422 has the same or close to the same refractive index as the material forming the grating area 422, thereby de-functionalizing the grating. In some embodiments, the same material is used for both the grating and the planarizing polymer.

[0062] The polymer layer 440 can be cast to a height higher than the height of the metalized ICG area 423. In some embodiments, the polymer layer 440 can cover the metalized ICG area 423 to a depth 430 in the range of 10 nm to 100 nm, e.g., (e.g., 10 nm or more, 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, e.g., 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less).

[0063] Other implementations of grating de-functionalization can be considered. For example, Figure 5A and 5B An example process of de-functionalization of a super-sized surface grating area 524 corresponding to an OCE is shown. Figure 5A A cross-sectional view of a master polymer wafer 510 made of a first material 512 having a first super-sized surface grating area 524 and an ICG 530 is shown, as Figure 3 indicated.

[0064] Figure 5B ​This illustrates the defunctionalization of unwanted OCE surface grating regions through planarization. Oversized surface grating regions 524 can be defunctionalized by casting another polymer layer to planarize them outside the selected functional OCE regions. Typically, the polymer used to planarize the grating region 524 has the same or nearly the same refractive index as the material forming the grating region 524, thereby defunctionalizing the grating. In some embodiments, the same material is used for both the grating and the planarizing polymer.

[0065] like Figure 5B As shown, after planarizing the oversized surface grating region 524, only selected OCE grating regions 550 may be retained. The polymer layer 540 can be cast to a height greater than the height of the oversized surface grating region 524. In some embodiments, the polymer layer 540 may cover the oversized surface grating region 528 to a depth 530 as previously described.

[0066] Several methods may exist to defunctionalize the grating regions on the host polymer wafer through planarization. In some embodiments, planarization can be accomplished by depositing polymer resin droplets and subsequently pressing the droplets into a homogeneous layer to defunctionalize the underlying grating. Figure 6 illustrates such a defunctionalization method.

[0067] Figure 6A A cross-sectional view of a main polymer wafer 610 with a surface grating region 620 is shown, on which multiple resin droplets 635 have been deposited in a pattern and volume sufficient to fill the region to be defunctionalized. Figure 6B A top view of the same master polymer wafer 610 with deposited resin droplets 635 is shown. The surface grating region 620 may correspond to an oversized ICG or OCE surface grating region as described above. The resin droplets 635 have the same or nearly the same refractive index as the material forming the surface grating region 620.

[0068] The process described is in Figure 6C The process continues in the cross-sectional view. Then, resin droplets 635 are brought into contact with a flat surface 645, and pressure 670 is applied, causing resin droplets 634 to diffuse and form a defunctionalized region 655, leaving a portion of the surface grating region 620 unchanged. The defunctionalized region 655 is then cured with ultraviolet (UV) light 660.

[0069] like Figure 6D As shown, the flat surface 645 is then removed, leaving the selected raster region 620 outside the defunctionalized region 655 unchanged. Figure 6EA top view example of the de-functionalized region 655 is shown after the resin droplet 635 has spread and cured to produce the de-functionalized region 655. In some embodiments, the de-functionalized region 655 can be smaller than the total surface grating region 620.

[0070] Figures 7A to 7C An alternative method of de-functioning a grating region on a master polymer wafer is shown. The de-functioning shown can be achieved by using a press mold, heat, and pressure to press down and flatten selected gratings to the height of the master polymer wafer.

[0071] Figure 7A A cross-sectional view of a master polymer wafer 710 with a super-size surface grating region 720 to be de-functionalized is shown. In some embodiments, the master polymer wafer 710 can be cured below the cross-linking threshold of the selected material (e.g., 70% for a suitable thiophene-based polymer) so that the material can still be easily deformed.

[0072] Reference Figure 7B The master polymer wafer 710 is in contact with a heated stage 780. In some embodiments, the stage 780 can be heated to a range between 60°C and 120°C (e.g., between 60°C and 100°C, between 60°C and 80°C, between 80°C and 100°C, between 80°C and 120°C). The stage 780 is heated to a temperature such that the master polymer wafer 710 material can be deformed under pressure without melting the super-size surface grating region 720.

[0073] A press mold 790 with a void 750 is positioned above the master polymer wafer 710 to align the void 750 with a selected region of the super-size surface grating region 720. The press mold 790 is shown with a larger lateral dimension than the super-size surface grating region 720. In general, the press mold can be made of a material of sufficient hardness so as to flatten the super-size surface grating region 720 without itself deforming (e.g., metal).

[0074] Figure 7B The depth of the void 750 of the press mold 790 is greater than the super-size surface grating region 720. In this way, the super-size surface grating region 710 under the void 750 remains unchanged after pressure is applied. The press mold 790 is shown with one void 750, but there can be more (e.g., two, three, four, or more), depending on how many discrete grating regions are needed.

[0075] The die 790 contacts the main polymer wafer 710, while the wafer is heated by the heating stage 780. Sufficient pressure 770 is applied to planarize a portion of the oversized surface grating region 720 (i.e., not aligned with the gap 750) that is in contact with the die 790, in order to defunctionalize these regions.

[0076] like Figure 7C As shown, the die 790 is removed from the main polymer wafer 710 and the main polymer wafer 710 is removed from the stage 780, leaving only the selected surface grating area 721.

[0077] although Figures 7A-7C A die 790 with a single void 750 of uniform depth is shown, such that the portion of the grating aligned with the void does not deform. However, in some embodiments, the void 750 may be designed to imprint a pattern different from the pattern originally cast into the main polymer wafer 710 into the oversized surface grating region 720.

[0078] For example, grating embedding in a die can be used to modify or replace a portion of an oversized surface grating region on the host polymer wafer. The embedded grating can have a pitch, depth, duty cycle, or orientation different from the oversized surface grating region originally cast into the host polymer wafer. In some embodiments, the embedded grating can include a combination of these modifications. Using a die with an embedded grating, a portion of the oversized surface grating region can be defunctionalized while the remainder is refunctionalized. Figure 8A -8C shows a die with an embedded grating having an ultra-large surface grating region for modifying the main polymer wafer.

[0079] Figure 8A A cross-sectional view of a main polymer wafer 810 with an oversized surface grating region 820 to be modified is shown. Figure 8B shows a die 890 with embedded gratings 852 positioned above the main polymer wafer 810 such that the embedded gratings 852 are aligned with selected portions of the oversized surface grating region 820 to be refunctionalized. The die 890 is shown as having one embedded grating 852, although this is typically the case, but the die 890 may have more than one embedded grating 852 (e.g., two, three, or four or more). In some embodiments, the die 890 may have a combination of embedded gratings and uniform voids.

[0080] The die 890 is then brought into contact with the heated main polymer wafer 810 on the stage 880. Pressure 870 is applied to the die 890 to defunctionalize the oversized surface grating region 820 that is not located below the embedded grating 852 and to refunctionalize the remaining surface grating region 821.

[0081] As shown in FIG. 8C, the mold 890 is then removed from the master polymer wafer 810, and the master polymer wafer 810 is removed from the stage 880, leaving only the master polymer wafer 810 with the re-functionalized surface grating region 821.

[0082] Figure 9 The above process is summarized, showing a flowchart of an example singulation process 900 for producing multiple eyepieces from a master polymer wafer. The singulation process 900 begins with casting a master polymer wafer with one or more oversized surface grating regions corresponding to the gratings required for ICGs or OCEs (902). An example of a master polymer wafer including oversized ICG gratings is shown in FIG. 9A, and an example of a master polymer wafer including oversized OCE gratings is shown in FIG. 9B. These oversized surface grating regions can provide control over one or more design parameters in the final eyepiece, including varying IPD length, OCG diameter, or center-to-center distance. Figure 2 Figure 3 The singulation process 900 then proceeds to de-functionalize one or more surface grating regions on the master polymer wafer 210 (904). The de-functionalization process for a master polymer wafer with oversized ICG surface grating regions is accomplished by metallizing the selected surface grating regions and casting new polymer material to cover the surface grating regions. The de-functionalization process for a master polymer wafer with oversized OCE surface grating regions can be accomplished by casting new polymer material or by using a heated jig and mold.

[0083] The master polymer wafer with oversized ICG surface grating regions is first metallized on a portion of its region corresponding to the light input from the projector (906). The metallized region is further positioned to control the center-to-center distance between the ICG and OCE after singulation.

[0084] After metallizing a portion of the oversized ICG surface grating region, the remaining region is de-functionalized by casting new polymer material to a depth sufficient to cover the metallized region and flatten the remaining surface grating (907).

[0085] Turning now to a master polymer wafer cast to have one or more oversized OCE surface grating regions, a portion of the grating region is de-functionalized by planarization (908). Planarization can be accomplished by a combination of heat and pressure or by casting new polymer material over the selected region.

[0086] As shown in FIG. 9B, the master polymer wafer 910 is then metallized on a portion of its region corresponding to the light input from the projector 920 (910). The metallized region is further positioned to control the center-to-center distance between the ICG and OCE after singulation.

[0087] As shown in FIG. 9B, the master polymer wafer 910 is then metallized on a portion of its region corresponding to the light input from the projector 920 (910). The metallized region is further positioned to control the center-to-center distance between the ICG and OCE after singulation. Figures 6A-6E ​A first example of planarizing a portion of the oversized OCE surface grating region is shown in FIGS. 8A-8C by depositing resin droplets. A pattern of resin droplets is deposited on the selected portion and pressed into a planar layer with a flat surface. The resin is then cured with UV light and the flat surface is removed, thereby defunctionalizing the selected region of the oversized OCE surface grating region.

[0088] Alternatively, planarizing a portion of the oversized OCE surface grating region is accomplished by using a press mold, as shown in FIGS. 9A-9C. Figures 7A-7C and Figure 8A In both examples, the master polymer wafer having the oversized OCE surface grating region to be defunctionalized is placed on a heated stage and heated to a temperature at which the polymer material of the wafer is malleable. A press mold is then placed over the surface grating region to be defunctionalized. In the example of FIGS. 8A-8C, the press mold includes a void having a depth greater than the oversized surface grating region, such that a selected portion of the grating region remains unmodified. Figures 7A-7C Figure 8A The example of FIGS. 8A-8C includes one or more embedded grating patterns to defunctionalize the portion and refunctionalize the remaining surface grating region.

[0089] The press mold is then brought into contact with the master polymer wafer and pressure is applied to defunctionalize the selected surface grating region not located under the void, or optionally, to refunctionalize the region under the embedded grating. The press mold is then removed, leaving the selected surface grating region or the newly refunctionalized surface grating region.

[0090] After defunctionalization of the one or more oversized surface grating regions, the one or more eyepieces are then singulated from the master polymer wafer (910). Typically, the eyepieces can be singulated to control the spacing between the ICG and the OCE and the positioning of the OCE within the eyepiece region to account for a particular IPD. The eyepieces can then be further processed as needed and assembled into a head-mounted display.

[0091] A number of embodiments have been described. Other embodiments are within the following claims.​

Claims

1. A method comprising: A wafer is provided, the wafer including a first surface grating extending over a first region of the surface of the wafer and a second surface grating extending over a second region of the surface of the wafer; At least a portion of either the first surface grating in the first surface grating region or the second surface grating in the second surface grating region is defunctionalized, wherein the defunctionalized portion of the surface grating is retained but no longer used as a grating; and The eyepiece is segmented from the wafer, the eyepiece comprising a portion of the first surface grating region and a portion of the second surface grating region. Wherein, the first surface grating in the eyepiece corresponds to the input coupling grating for the head-mounted display, and the second surface grating corresponds to the pupil expander grating for the head-mounted display.

2. The method according to claim 1, wherein, Defunctionalizing a portion of at least one of the first surface grating in the first surface grating region or the second surface grating in the second surface grating region includes: planarizing the portion of the corresponding surface grating.

3. The method according to claim 2, wherein, Planarizing a portion of at least one of the first surface grating in the first surface grating region or the second surface grating in the second surface grating region includes casting material over the corresponding portion of the surface grating.

4. The method according to claim 3, wherein, The material being cast is the same material as the material forming the surface grating.

5. The method according to claim 4, wherein, The material is a polymer material.

6. The method according to claim 1, further comprising: A reflective material is deposited on a portion of the first surface grating.

7. The method according to claim 6, wherein, The reflective material is metal.

8. The method according to claim 1, wherein, The height of the defunctionalized portion in the first surface grating region or the second surface grating region above the surface is greater than the height of the first surface grating or the second surface grating.

9. The method according to claim 8, wherein, The height of the defunctionalized portion is no more than 100 nm higher than the height of the corresponding surface grating.

10. The method according to claim 1, wherein, Providing the wafer includes: imprinting the first surface grating and the second surface grating onto the surface of the wafer.

11. The method according to claim 1, wherein, Providing the wafer includes: casting a wafer having the first surface grating and the second surface grating.

12. The method according to claim 1, wherein, The second region has a minimum lateral dimension greater than 30 mm.

13. The method according to claim 1, wherein, The pupil expander grating has a maximum lateral dimension of 30 mm or less.

14. The method according to claim 1, wherein, The input coupling grating has a maximum lateral dimension of 5 mm or less.

15. The method according to claim 1, further comprising: The eyepiece is assembled into a head-mounted display.

16. An article comprising: A planar waveguide formed of a polymer material, the planar waveguide including a first surface, the first surface including: First surface grating; A second surface grating spaced apart from the first surface grating; and The smooth portion between the first surface grating and the second surface grating. The smoothing portion includes a first region at a first surface height, wherein the first surface grating and the second surface grating each extend above the first surface height, and the smoothing portion includes a second region adjacent to the first surface grating or the second surface grating, the second region extending above the height of the adjacent first surface grating or the second surface grating, wherein the second region extends laterally over the defunctionalized portion of the first surface grating or the second surface grating by a distance greater than the pitch of the grating, and the defunctionalized portion is no longer used as a grating.

17. The article of claim 16, further comprising: A reflective layer supported by the first surface grating.

18. The article of claim 17, wherein, The first surface grating and the reflective layer are configured to couple incident light into the planar waveguide, thereby propagating toward the second surface grating.

19. The article of claim 16, wherein, The second surface grating is configured to extract light guided by the planar waveguide from the planar waveguide.

20. The article of claim 16, wherein, The second region extends 100 nm or less above the adjacent first surface grating and second surface grating.

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