FABRICATION OF AN OPTICAL WEDGE
Various embodiments are disclosed relating to fabrication of an optical wedge. For example, one embodiment provides a method for manufacturing an optical wedge comprising inserting a wedge blank into a vacuum molding tool and applying a vacuum to the vacuum molding tool to temporarily hold the wedge blank against a molding surface of the vacuum molding tool. The method further comprises removing a layer from a top surface of the wedge blank to expose a machined surface of the wedge blank, and casting a finish layer on the machined surface to form a finish layer of a finished optical wedge.
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This application is a divisional of U.S. patent application Ser. No. 12/779,790, filed on May 13, 2010, and titled “FABRICATION OF AN OPTICAL WEDGE” which claims priority to U.S. Provisional Application No. 61/309,702, filed Mar. 2, 2010. The above-listed applications are hereby incorporated by reference in their entireties for all purposes.
BACKGROUNDAn optical wedge is a wedge-shaped light guide configured to transmit light between a first light interface located at an end of the light guide and a second light interface located at a major face of the light guide via total internal reflection. Such guides may be image-retaining where there is a one-to-one correspondence between an angle of image light at the edge and a position of the image light at a surface of the wedge. Thus, light input into the first light interface within a suitable range of input angles propagates through the optical wedge until the critical angle of internal reflection is reached, thereby allowing the light to be transmitted out of the optical wedge through the second interface. Depending upon the design of a particular optical wedge, the first light interface may be either at a thin end or a thick end of the optical wedge. In either case, the internal reflection of light within the optical wedge allows light to fan out to a desired beam size within a relatively small volume of space, and therefore may permit the construction of a relatively compact optical system compared to a similar system without an optical wedge.
SUMMARYVarious embodiments are disclosed herein that relate to fabrication of an optical wedge. For example, one embodiment provides a method for manufacturing an optical wedge, the method comprising inserting a wedge blank into a vacuum molding tool and applying a vacuum to the vacuum molding tool to temporarily hold a surface of the wedge blank against a surface of the vacuum molding tool. The method further comprises removing a layer from a top surface of the wedge blank to expose a machined surface of the wedge blank, and casting a finish layer on the machined surface to form a finished optical wedge.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.
As described above, surface smoothness and dimensional accuracy may be goals in the fabrication of an optical wedge. In some applications, a thickness tolerance of approximately 1% of the maximum thickness of the wedge may be needed to achieve desired optical performance. For example, surface ripples having a period approaching a magnitude of a beam width of a projection device may cause degradation in image focus, which may be magnified over the course of multiple reflections from the rippled surface. Accordingly, in some applications, surface roughness may be controlled to 1 micron per 20 mm maximum gradient deviation.
However, manufacturing an optical wedge with such properties may pose various challenges. For example, a PMMA (poly(methyl methacrylate)) extruded optical wedge may have surface roughness on the order of 10 nm RA arising from the extrusion aperture, which is well above the <2 nm RA desired for some applications. An optical wedge cast between two float glass sheets may have acceptable smoothness. However, PMMA may shrink by approximately 12-24% during curing. Due to the non-uniform thickness of an optical wedge, this shrinkage may result in poor thickness profile tolerance, leading to loss of functionality.
Accordingly, various embodiments are provided herein that relate to manufacturing an optical wedge in a manner that may help to avoid such issues. It will be appreciated that the schematic views presented herein are greatly exaggerated for illustrative purposes. Further, it will be appreciated that the wedge profiles presented in these exaggerated schematic views are merely example wedge profiles, and that any suitable wedge profile may be achieved within the scope of the present disclosure.
Wedge blank 150 may have any suitable dimensions. For example, in some non-limiting example embodiments, wedge blank 150 may have a pre-processing thickness of approximately 1 mm-20 mm. Because some acrylic polymerization processes result in approximately 12%-24% shrinkage of the acrylic material as the polymerization reactions progress, it will be appreciated that a thicker initial charge of monomer may be used in some embodiments to achieve such a final thickness for wedge blank 150.
Vacuum molding tool 102 includes one or more vacuum ports 106 fluidly connected to a vacuum pump (not shown) and configured to channel air and/or other gases from the vacuum molding tool 102 toward the vacuum pump. It will be appreciated that any suitable vacuum pump may be employed within the scope of the present disclosure. In some embodiments, vacuum molding tool 102 may be mounted on a stabilized surface, such as an optical mount platform, to provide a level surface for the molding and casting operations described in more detail.
Vacuum molding tool 102 also includes a molding surface 104 configured to provide a form for shaping a molded surface of the optical wedge into a desired profile. For example, in
In some embodiments, molding surface 104 may include one or more local topographic characteristics 108, each of which is configured to impart a corresponding complementary topographic feature to the finished optical wedge. For example, in the scenario shown in
Method 200 comprises, at 202, inserting a wedge blank into a vacuum molding tool. For example,
Continuing, method 200 comprises, at 206, removing a portion of the top surface of the wedge blank while the vacuum molding tool is still under vacuum. For example,
The machined surface of the wedge blank may have a surface roughness greater than desired for some applications of the finished optical wedge. Thus, method 200 comprises, at 208, casting a finish layer in-situ on the machined surface of the wedge blank while the vacuum molding tool is still under vacuum. For example,
Accordingly, process 208 may comprise, at 210, depositing a precursor for the finish layer on the machined surface of the wedge blank. Thus, in a scenario where the finish layer is PMMA, methyl methacrylate monomer (MMA) may be deposited on machined surface 406 for subsequent polymerization into PMMA. This deposition may be performed in any suitable fashion. For example, in some embodiments, liquid precursor material may be deposited via pouring, spraying in a pattern, injected in preparation for a reaction injection molding process, etc. Further, the precursor may be deposited in any suitable thickness to achieve a final finish layer thickness suited to an application of the finished optical wedge. For example, in one scenario, 100 microns thickness of precursor may be deposited on the machined surface. Alternatively, in some embodiments, the precursor may be a molten thermoplastic polymer of suitable refractive index formulated for injection molding of finish layer 502.
It will be appreciated that any suitable precursor formulation may be used. For example, in some embodiments, a mixture of precursor materials, such as a monomer and a suitable solvent may be combined to create a precursor formulation having a viscosity within a range of approximately 10 cp-400 cp. Formulations within the higher viscosity end of this range may be easy to handle during the deposition process, while formulations within the lower viscosity end of this range may more readily wet the machined surface, etc. It will be appreciated that this range is merely illustrative, and that any suitable viscosity achieved by any suitable precursor formulation may be utilized.
Continuing, 208 may further comprise, at 212, positioning and retaining, such as by clamping, a casting plate in continuous contact with a top surface of the precursor while the vacuum molding tool is still under vacuum. For example,
Casting plate 504 may be any suitable material exhibiting a surface roughness characteristic to be imparted onto a diffuser interface surface 510 of finish layer 502. For example, in some embodiments, casting plate 504 is a glass plate, such as a borosilicate float glass plate, having an average surface roughness of approximately 2 nm RA or less. Further, in some embodiments, casting plate 504 may be configured to avoid bowing, so that diffuser interface surface 510 is approximately flat on the finished optical wedge. For example, in one scenario, casting plate 504 may be approximately 20 mm-25 mm thick to provide structural rigidity and avoid bowing or deflection in casting plate 504. In another scenario, the casting plate may include one or more structural ribs, members, etc. (not shown) to provide structural rigidity.
In some embodiments, a finish layer interface surface of casting plate 504 may be conditioned with a mold release agent adsorbed to the finish layer interface surface of the casting plate. The mold release agent may be configured to repel the precursor formulation. For example, the mold release agent may be a suitable silicone compound or a fluorocarbon compound, though it will be appreciated that other suitable mold release agents may be employed within the scope of the present disclosure. In some embodiments, casting plate 504 is separated from wedge blank 150 only by finish layer 502 so that an edge bead is formed, while in other embodiments, a gasket may be included around a perimeter of casting plate 504 to avoid formation of an edge bead. For example, in an embodiment where molten polymer is used as a precursor, a gasket may be included to provide a space between machined surface 406 and casting plate 504 to facilitate an injection molding process.
In some embodiments, electrostatic potentials of casting plate 504, vacuum molding tool 102, and/or wedge blank 150 may be controlled to avoid differential charging at machined surface 406 and/or at the finish layer interface surface of casting plate 504. This may beneficially enhance wetting of the precursor on machined surface 406 and/or the finish layer interface surface of casting plate 504, avoid bubble formation on said surfaces, etc. In one scenario, control of the electrostatic potentials may be via an electron flood supplied via ionizer gun 512. In other embodiments, any other suitable mechanism may be used to reduce electrostatic potential differences between surfaces.
Continuing, process 208 further comprises, at 214, curing the precursor. In the embodiment shown in
Method 200 next comprises, at 216, disconnecting the vacuum from the vacuum molding tool and removing the finished optical wedge from the vacuum molding tool. For example,
By way of illustrating the thickness characteristics imparted to the finished optical wedge,
It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated may be performed in the sequence illustrated, in other sequences, in parallel, or in some cases omitted. Likewise, the order of the above-described processes may be changed.
The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.
Claims
1. A vacuum molding system for forming an optical wedge from a wedge blank, the vacuum molding system comprising:
- a vacuum pump;
- a vacuum molding tool comprising one or more vacuum ports fluidly connected to the vacuum pump, the vacuum molding tool including a molding surface configured to temporarily shape a molded surface of the wedge blank under the urging of a pressure differential generated by the vacuum pump; and
- a casting plate configured to be retained across a finish layer of the wedge blank opposite from the molded surface of the wedge blank.
2. The vacuum molding system of claim 1, wherein the molding surface comprises an optical surface profile to be imparted to the molded surface of the wedge blank.
3. The vacuum molding system of claim 2, wherein the molding surface of the vacuum molding tool includes one or more local topographic characteristics each configured to impart a complementary local topographic feature to the molded surface of the wedge blank.
4. The vacuum molding system of claim 1, wherein the casting plate comprises a float glass plate configured to impart a planar surface to a diffuser interface surface of a finished optical wedge.
5. The vacuum molding system of claim 4, wherein the casting plate comprises a surface roughness average of two nanometers or less.
6. The vacuum molding system of claim 1, further comprising an ionizer gun configured to control one or more electrostatic potentials of the vacuum molding system.
7. The vacuum molding system of claim 1, further comprising a precursor-curing energy source.
8. The vacuum molding system of claim 7, wherein the precursor-curing energy source comprises an ultraviolet lamp.
9. The vacuum molding system of claim 1, further comprising a wedge blank inserted in the vacuum molding tool, the wedge blank comprising a smoother surface in contact with the molding surface and a rougher surface opposite the molding surface.
10. The vacuum molding system of claim 1, further comprising a finish layer applied over the wedge blank, wherein the casting surface is in contact with the finish layer.
11. The vacuum molding system of claim 1, wherein the casting surface comprises a mold release agent.
12. The vacuum molding tool of claim 1, wherein the casting plate has a thickness of 20-25 mm.
13. An optical wedge, comprising:
- a wedge blank comprising a surface having a non-planar shape; and
- a cured polymer disposed on a surface of the wedge blank opposite the surface having the non-planar shape, wherein the cured polymer comprises an index of refraction of within +/−0.01 of an index of refraction of the wedge blank, and wherein the cured polymer comprises a cast surface.
14. The optical wedge of claim 13, wherein the cast surface comprises a surface roughness average of two nanometers or less.
15. The optical wedge of claim 13, wherein the cast surface is planar, and wherein the surface having the non-planar shape comprises an aspheric optical feature.
16. The optical wedge of claim 13, wherein the cured polymer comprises poly(methyl methacrylate).
17. A vacuum molding system for forming an optical wedge from a wedge blank, the vacuum molding system comprising:
- a vacuum pump;
- a vacuum molding tool comprising one or more vacuum ports fluidly connected to the vacuum pump, the vacuum molding tool including a molding surface configured to temporarily shape a molded surface of the wedge blank under the urging of a pressure differential generated by the vacuum pump, the molding surface defining an aspheric optical feature; and
- a casting plate configured to be retained across a finish layer of the wedge blank opposite from the molded surface of the wedge blank.
18. The vacuum molding system of claim 17, wherein the casting plate comprises a float glass plate.
19. The vacuum molding system of claim 17, wherein the casting plate has a thickness of 20-25 mm.
20. The vacuum molding system of claim 18, further comprising an ionizer gun.
Type: Application
Filed: Feb 7, 2014
Publication Date: Jun 5, 2014
Applicant: Microsoft Corporation (Redmond, WA)
Inventors: Kurt Allen Jenkins (Sammamish, WA), Timothy Large (Bellevue, WA), Rajesh Manohar Dighde (Redmond, WA)
Application Number: 14/175,307
International Classification: B29D 11/00 (20060101); G02B 6/10 (20060101); B29C 59/00 (20060101);