BACKGROUND

Field

[0001] Embodiments of the present disclosure generally relate to waveguides for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide for methods of waveguide fabrication.

Description of the Related Art

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

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

[0004] One such challenge is displaying a virtual image overlayed on an ambient environment. Waveguides are used to assist in overlaying images. Generated light is propagated through a waveguide until the light exits the waveguide and is overlayed on the ambient environment. Fabricating waveguides can be challenging as waveguides tend to have non-uniform properties. Accordingly, what is needed in the art are improved augmented waveguides and methods of fabrication. SUMMARY

[0005] In one embodiment, a method of fabricating a waveguide structure is provided. The method includes imprinting a stamp into a resist. The stamp has a positive waveguide pattern including at least one pattern portion. The imprinting forms a negative waveguide structure that includes an inverse region with a residual layer. The resist is disposed on a surface of a portion of a substrate and the substrate has a first refractive index. The resist is cured on the surface of the substrate. The stamp is released and the residual layer is removed. A coating is deposited. The coating has a second refractive index substantially matched to or greater than the first refractive index of the surface of the substrate. The resist is removed form a waveguide structure including a region.

[0006] In another embodiment, a method of fabricating a waveguide structure is provided. The method includes depositing a coating having a second refractive index on a negative waveguide structure of a stamp. The second refractive index is substantially matched to or greater than a first refractive index of a substrate. The negative waveguide structure includes an inverse region. The coating is planarized and bonded to a surface of a portion of the substrate. The stamp is released to form a waveguide structure including a region.

[0007] In yet another embodiment, a method of fabricating a waveguide structure is provided. The method includes depositing a coating having a second refractive index between 1.5 and 2.5 on a negative waveguide structure of a stamp. The coating is substantially planar on the negative waveguide structure. The second refractive index is substantially matched to or greater than a first refractive index between 1.5 and 2.5 of a substrate. The negative waveguide structure includes an inverse input coupling region and an inverse output coupling region. The coating is bonded to a surface of a portion of the substrate. The surface of the substrate has an optical adhesive disposed thereon with a third refractive index substantially matched to the first refractive index and the second refractive index. The stamp is released to form a waveguide structure having a region. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, may admit to other equally effective embodiments.

[0009] Figure 1 is a perspective, frontal view of a waveguide combiner according to an embodiment.

[0010] Figure 2 is a flow diagram illustrating operations of a method for fabricating a waveguide structure according to an embodiment.

[0011] Figures 3A-3F are schematic, cross-sectional views of an waveguide structure during a method for fabricating a waveguide structure according to an embodiment.

[0012] Figure 4 is a flow diagram illustrating operations of a method for fabricating a waveguide structure according to an embodiment.

[0013] Figures 5A-5D are schematic, cross-sectional views of an waveguide structure during a method for fabricating a waveguide structure according to an embodiment.

[0014] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical 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.

DETAILED DESCRIPTION

[0015] Embodiments described herein relate to methods for fabricating waveguide structures. The methods described herein enables the fabrication of waveguide structures having input coupling regions, waveguide regions, and output coupling regions formed from inorganic or hybrid (organic and inorganic) materials. [0016] Figure 1 is a perspective, frontal view of a waveguide combiner 100. It is to be understood that the waveguide combiner 100 described below is an exemplary waveguide combiner. The waveguide combiner 100 includes an input coupling region 102 defined by a plurality of gratings 108, a waveguide region 104, and an output coupling region 106 defined by a plurality of gratings 110.

[0017] The input coupling region 102 receives incident beams of light (a virtual image) having an intensity from a microdisplay. Each grating of the plurality of gratings 108 splits the incident beams into a plurality of modes, each beam having a mode. Zero-order mode (TO) beams are refracted back or lost in the waveguide combiner 100, positive first-order mode (T1) beams undergo total-internal-reflection (TIR) through the waveguide combiner 100 across and though the waveguide region 104 to the output coupling region 106, and negative first-order mode (T-1) beams propagate in the waveguide combiner 100 a direction opposite to the T1 beams. The T1 beams undergo total-internal-reflection (TIR) through the waveguide combiner 100 until the T1 beams come in contact with the plurality of gratings 110 in the output coupling region 106. The T1 beams contact a grating of the plurality of gratings 110 where the T1 beams are split into TO beams refracted back or lost in the waveguide combiner 100, T1 beams that undergo TIR in the output coupling region 106 until the T1 beams contact another grating of the plurality of gratings 110, and T-1 beams coupled out of the waveguide combiner 100.

[0018] Figure 2 is a flow diagram illustrating operations of a method 200 for fabricating a waveguide structure 300 as shown in Figures 3A-3F. In one embodiment, waveguide structure 300 corresponds to at least one of the input coupling region 102, the waveguide region 104, and the output coupling region 106 of the waveguide combiner 100. In another embodiment, the waveguide structure 300 corresponds to a master of at least one of the input coupling region 102, the waveguide region 104, and the output coupling region 106 of the waveguide combiner 100. At operation 201 , a stamp 308 having a positive waveguide pattern 310 is imprinted on a resist 326 that is disposed on a surface 306 a portion 302 of a substrate 304 to form a negative waveguide structure 312. The substrate 304 has a first refractive index. In one embodiment, the substrate 304 includes at least one of glass and plastic materials. [0019] As shown in Figure 3A, the positive waveguide pattern 310 includes at least one pattern portion 314 to result in the formation of at least one of the input coupling region 102, the waveguide region 104, and the output coupling region 106 of the waveguide combiner 100. As shown in Figure 3A and Figure 3B, the negative waveguide structure 312 includes an inverse region 316 having a residual layer 318, oftentimes referred to as a bottom surface. In one embodiment, the inverse region 316 includes a plurality of inverse gratings 320 to form at least one of a plurality of gratings 108 of the input coupling region 102, a plurality of gratings 110 of the output coupling region 106, and the waveguide region 104. In one embodiment, the inverse gratings 320 have inverse top surfaces 322 parallel to the surface 306 of the substrate 304, inverse sidewall surfaces 324, and the residual layer 318 parallel to the surface 306 of the substrate 304. In one embodiment, each of the inverse sidewall surfaces 324 of the inverse gratings 320 are oriented normal to the surface 306 of the substrate 304. In another embodiment, the each of the inverse sidewall surfaces 324 of the inverse gratings 320 are angled relative to the surface 306 of the substrate 304. In yet another embodiment, the portion of the inverse sidewall surfaces 324 are oriented normal and a portion of the inverse sidewall surfaces 324 of the inverse gratings 320 are angled relative to the surface 306 of the substrate 304.

[0020] At operation 202, the resist 326 on the surface 306 of the substrate 304 is cured to stabilize the resist 326. At operation 203, the stamp 308 is released from the resist 326. In one embodiment, the stamp 308 is fabricated from a waveguide master having a negative pattern that includes an inverse pattern portion. The stamp 308 is molded from the waveguide master. The stamp 308 includes a semi transparent material such as fused silica or polydimethylsiloxane (PDMS) to allow the resist 326 to be cured by exposure to electromagnetic radiation, such as infrared (IR) radiation or ultraviolet (UV) radiation. In one embodiment, the resist 326 includes a UV curable material (such as mr-N210 available from Micro Resist Technology) that is nano imprintable by the stamp 308 including PDMS. In one embodiment, the surface 306 of the substrate 304 is prepared for spin coating of the UV curable material by UV ozone treatment, oxygen (0 ₂ ) plasma treatment, or by application of a primer (such as mr-APS1 available from Micro Resist Technology). The resist 326 may alternatively be thermally cured. In another embodiment, the resist 326 includes a thermally curable material that may be cured by a solvent evaporation curing process that includes thermal heating or infrared illumination heating. The resist 326 may be disposed on the surface 306 using a liquid material pour casting process, a spin-on coating process, a liquid spray coating process, a dry powder coating process, a screen printing process, a doctor blading process, a physical vapor deposition (PVD) process, a chemical vapor deposition (CVD) process, a flowable CVD (FCVD) process, or an atomic layer deposition (ALD) process.

[0021] At operation 204, the residual layer 318 is removed. In one embodiment, the residual layer 318 is removed by plasma ashing, oftentimes referred to as plasma descumming, using an oxygen gas (0 ₂ ) containing plasma, a fluorine gas (F ₂ ) containing plasma, a chlorine gas (Cl ₂ ) containing plasma, and/or a methane (CH ₄ ) containing plasma. In another embodiment, a radio frequency (RF) power is applied to 0 ₂ and an inert gas, such as argon (Ar) or nitrogen (N), until the residual layer 318 is removed. As shown in Figure 3C, inverse gratings 320 have the inverse depths 328, 330 extending from the inverse top surfaces 322 to the surface 306 of the substrate 304. In one embodiment, the inverse depth 328 and the inverse depth 330 are substantially the same. In another embodiment, the inverse depth 328 and the inverse depth 328 are different.

[0022] At operation 205, a coating 322 is deposited on the surface 306 of the substrate 304. In one embodiment, as shown in Figure 3D and Figure 3E, the coating 322 is deposited on the surface 306 of the substrate 304 and the remaining projections of the negative waveguide structure 312. The coating 322 has a second refractive index substantially matched to or greater than the first refractive index. The coating 322 includes at least one of spin on glass (SOG), flowable SOG, sol-gel, organic nano imprintable, inorganic nano imprintable, and hybrid (organic and inorganic) nano imprintable materials, such as at least one of silicon oxycarbide (SiOC), titanium dioxide (Ti0 ₂ ), silicon dioxide (Si0 ₂ ), vanadium (IV) oxide (VO _x ), aluminum oxide (Al ₂ 0 ₃ ), indium tin oxide (ITO), zinc oxide (ZnO), tantalum pentoxide (Ta ₂ Os), silicon nitride (Si3N ₄ ), titanium nitride (TiN), and/or zirconium dioxide (Zr0 ₂ ) containing materials. The coating 322 may be disposed on the surface 306 using a liquid material pour casting process, a spin-on coating process, a liquid spray coating process, a dry powder coating process, a screen printing process, a doctor blading process, a PVD process, a CVD process, a FCVD process, or an ALD process. Furthermore, the coating 322, such as a SiOC coating, may undergo UV curing or thermal curing. As shown in Figure 3D, in one embodiment, excess coating 322 may be present. In embodiment, the excess coating 322 is removed using material thermal reflow or etching. As shown in Figure 3E, the coating 322 is flush with the remaining projections of the negative waveguide structure 312, or extends above the substrate 304 to the same height as the remaining projections of the negative waveguide structure 312. In one embodiment, the coating 322 is liquid deposited and the excess coating 322 is removed by mechanical planarization.

[0023] The refractive index of the coating 322 is tuned based on the first refractive index of the substrate 304 and the strength of gratings, such as the resulting plurality of gratings 108 of the input coupling region 102 and/or the resulting plurality of gratings 110 of the output coupling region 106 formed by the method 200. The refractive index of the coating 322 is tuned based on the first refractive index of the substrate 304 and the strength of gratings to control the in-coupling and out- coupling of light and facilitate light propagation through the waveguide structure 300. For example, the material of surface 306 of the substrate 304 has a first refractive index of between about 1.5 and about 2.5 and the material of the coating 322 has a second refractive index of between about 1.5 and about 2.5. By matching the refractive indices of the materials utilized to fabricate the substrate 304 and the material of the coating 322, light propagation through both the substrate 304 and the material of the coating 322 may be achieved without substantial light refraction at an interface between the surface 306 of the substrate 304 and the material of the coating 322. By utilizing the material of the coating 322 with a refractive index greater the refractive indices of the materials utilized to fabricate the substrate 304, more light will be in-coupled and out-coupled from the waveguide structure 300 through a light acceptance angle. The substrate 304 and the material of the coating 322 collectively comprise the waveguide structure 300. By utilizing materials having a refractive index of between about 1.5 and about 2.5 for the substrate 304, as compared to the refractive index of air (1.0), the total internal reflection, or at least a high degree thereof, is achieved to facilitate light propagation through the waveguide structure 300.

[0024] At operation 206, the resist 326 is removed to form the waveguide structure 300. In one embodiment, the resist 326 is removed by plasma ashing, using an 0 ₂ containing plasma, F ₂ containing plasma, a Cl ₂ containing plasma, and/or a CH ₄ containing plasma. In another embodiment, a RF power is applied to 0 ₂ and an inert gas, such as argon (Ar) or nitrogen (N), until the resist 326 is removed. As shown in Figure 3F, the waveguide structure 300 includes a region 334. In one embodiment, the region 334 corresponds to at least one of the input coupling region 102, the waveguide region 104, and the output coupling region 106 of a waveguide combiner 100. The region 334 includes a plurality of gratings 336. In one embodiment, the region 334 includes the plurality of gratings 336 corresponding to at least one of the plurality of gratings 108 of the input coupling region 102, the plurality of gratings 110 of the output coupling region 106, and the waveguide region 104. In one embodiment, the gratings 336 have top surfaces 338 parallel to the surface 306 of the substrate 304 and sidewall surfaces 340. In one embodiment, each of the sidewall surfaces 340 of the gratings 336 are oriented normal to the surface 306 of the substrate 304. In another embodiment, each of the sidewall surfaces 340 of the gratings 336 are angled relative to the surface 306 of the substrate 304. In yet another embodiment, the a portion of the sidewall surfaces 340 are oriented normal and a portion of the sidewall surfaces 340 of the gratings 336 are angled relative to the surface 306 of the substrate 304. In one embodiment, the sidewall surfaces 340 are angled at an angle of between about 15 degrees and about 75 degrees. The gratings 336 have the depths 342, 344 extending from the surface 306 of the substrate 304 to the top surfaces 338. In one embodiment, the depth 342 and the depth 344 are substantially the same. In another embodiment, the depth 342 and the depth 344 are different.

[0025] Figure 4 is a flow diagram illustrating operations of a method 400 for fabricating a waveguide structure 500 as shown in Figures 5A-5D. In one embodiment, waveguide structure 500 corresponds to at least one of the input coupling region 102, the waveguide region 104, and/or the output coupling region 106 of the waveguide combiner 100. In another embodiment, the waveguide structure 500 corresponds to a master of at least one of the input coupling region 102, the waveguide region 104, and the output coupling region 106 of the waveguide combiner 100. At operation, 401 a coating 322 is deposited on a negative waveguide structure 512 of a stamp 308. As shown in Figure 5A, in one embodiment, the deposited coating 322 is conformal to the negative waveguide structure 512 of the stamp 308. As shown in Figure 5B, in one embodiment, the deposited coating 322 is substantially planar to the negative waveguide structure 512 of the stamp 308. Therefore, it is not necessary to planarize the coating 322 at optional operation 402. At optional operation 402, in one embodiment, planarizing the coating 322 includes mechanical leveling by gravity, thermal reflow, or chemical mechanical polishing (CMP).

[0026] The stamp 308 is molded from waveguide master and may be made from a semi-transparent material such as fused silica or PDMS material to allow the coating 322 to be cured by exposure to electromagnetic radiation, such as IR radiation or UV radiation. In one embodiment, the stamp 308 comprises a rigid backing sheet, such as a sheet of glass, to add mechanical strength to facilitate deposition and planarization of the coating 322.

[0027] The coating 322 includes at least one of SOG, flowable SOG, sol-gel, organic nano imprintable, inorganic nano imprintable, and hybrid (organic and inorganic) nano imprintable materials, such as at least one of SiOC, Ti0 ₂ , Si0 ₂ , VO _x , Al ₂ 03, ITO, ZnO, Ta ₂ Os, S13N4, TiN, and Zr0 ₂ containing materials. The coating 322 may be deposited using a liquid material pour casting process, a spin-on coating process, a liquid spray coating process, a dry powder coating process, a screen printing process, a doctor blading process, a PVD process, a CVD process, a FCVD process, or an ALD process. In one embodiment, the coating material is doped with a dopant material in order to lower a melting temperature of the coating material and to allow for improved flow of the coating material during planarization. The dopant material may include a phosphorus (P) containing material and/or a boron (B) containing material that allow for thermal reflow at a lower temperature. [0028] As shown in Figure 5A and Figure 5B, the negative waveguide structure 512 includes an inverse region 516. The inverse region 516 includes a plurality of inverse gratings 520 to form at least one of a plurality of gratings 108 of the input coupling region 102, a plurality of gratings 110 of the output coupling region 106, and the waveguide region 104. In one embodiment, the inverse gratings 520 have inverse top surfaces 522 parallel to a bottom surface 521 of the stamp 308, inverse sidewall surfaces 524, and inverse bottom surfaces 523 parallel to the bottom surface 521 of the stamp 308. In one embodiment, each of the inverse sidewall surfaces 524 of the inverse gratings 520 are oriented normal to the bottom surface 521 of the stamp 308. In another embodiment, the each of the inverse sidewall surfaces 524 of the inverse gratings 520 are angled relative to the bottom surface 521 of the stamp 308. In another embodiment, inverse gratings 520 are blazed inverse angled gratings including include inverse blazed surfaces 502 angled relative to the bottom surface 521 of the stamp 308 and inverse sidewall surfaces 524 oriented normal to the bottom surface 521 of the stamp 308. In yet another embodiment, the inverse region 516 includes blazed inverse angled gratings and the plurality of inverse gratings 520 with a portion of the inverse sidewall surfaces 524 oriented normal and a portion of the inverse sidewall surfaces 524 of the inverse gratings 520 angled relative to the bottom surface 521 of the stamp 308. As shown in Figure 5A and Figure 5B, inverse gratings 520 have the inverse depths 528, 530 extending from the inverse top surfaces 522 to the bottom surface 521 of the stamp 308. In one embodiment, the inverse depth 528 and the inverse depth 530 are substantially the same. In another embodiment, the inverse depth 528 and the inverse depth 530 are different.

[0029] At operation 403, as shown in Figure 5C, the coating 322 is bonded to a surface 306 of a portion 302 of a substrate 304. An optical adhesive 501 is used to bond the coating 322 to the surface 306 of the substrate 304. In one embodiment, the optical adhesive 501 may contain a transparent metal oxide material or a clear acrylic polymer. The optical adhesive 501 has a third refractive index.

[0030] The coating 322 has a second refractive index substantially matched to or greater than a first refractive index of the substrate 304. The second refractive index of the coating is tuned based on the first refractive index of the substrate 304 and the strength of gratings, such as the resulting plurality of gratings 108 of the input coupling region 102 and/or the resulting plurality of gratings 110 of the output coupling region 106 formed by the method 400. The refractive index of the coating 322 is tuned based on the first refractive index of the substrate 304 and the strength of gratings to control the in-coupling and out-coupling of light and facilitate light propagation through the waveguide structure 500. Also, the optical adhesive 501 has a third refractive index substantially matched to the first refractive index and the second refractive index. For example, the material of surface 306 of the substrate 304 has a first refractive index of between about 1.5 and about 2.5, the material of optical adhesive 501 has a third refractive index of between about 1.5 and about 2.5, and the material of the coating 322 has a second refractive index of between about 1.5 and about 2.5. By matching the refractive indices of the materials utilized to fabricate the substrate 304, the material of optical adhesive 501 , and the material of the coating 322, light propagation through the substrate 304, the material of optical adhesive 501 , and the material of the coating 322 may be achieved without substantial light refraction at an interface between substrate 304, the material of optical adhesive 501 , and the material of the coating 322. By utilizing the material of the coating 322 with a refractive index greater the refractive indices of the materials utilized to fabricate the substrate 304, more light will be in-coupled and out-coupled from the waveguide structure 500 through a light acceptance angle. By utilizing materials having a refractive index of between about 1.5 and about 2.5 for the substrate 304 and the material of optical adhesive 501 , as compared to the refractive index of air (1.0), the total internal reflection, or at least a high degree thereof, is achieved to facilitate light propagation through the waveguide structure 500.

[0031] At operation 404, the stamp 308 is released to form the waveguide structure 500. As shown in Figure 5D, the waveguide structure 500 includes a region 534. In one embodiment, the region 534 corresponds to at least one of the input coupling region 102, the waveguide region 104, and the output coupling region 106 of a waveguide combiner 100. The region 534 includes a plurality of gratings 536. In one embodiment, the plurality of gratings 536 corresponds to at least one of the plurality of gratings 108 of the input coupling region 102, the plurality of gratings 110 of the output coupling region 106, and the waveguide region 104. In one embodiment, the gratings 536 have top surfaces 538 parallel to the surface 306 of the substrate 304 and sidewall surfaces 540. In one embodiment, each of the sidewall surfaces 540 of the gratings 536 are oriented normal to the surface 306 of the substrate 304. In another embodiment, the each of the sidewall surfaces 540 of the gratings 536 are angled relative to the surface 306 of the substrate 304. In another embodiment, gratings 536 are blazed angled gratings including blazed surfaces 506 angled relative to the surface 306 of the substrate 304 and sidewall surfaces 540 oriented normal to the surface 306 of the substrate 304. In yet another embodiment, the region 534 includes blazed angled gratings and the gratings 536 with a portion of the sidewall surfaces 540 oriented normal and a portion of the sidewall surfaces 540 of the gratings 536 angled relative to the surface 306 of the substrate 304. The gratings 536 have the depths 542, 544 extending from the optical adhesive 501 to the top surfaces 538. In one embodiment, the depth 542 and the depth 544 are substantially the same. In another embodiment, the depth 542 and the depth 544 are different.

[0032] In summation, methods for fabricating waveguide combiners are described herein. The methods provide for waveguide combiners having input coupling regions, waveguide regions, and output coupling regions formed from inorganic or hybrid (organic and inorganic) materials that define fine light gratings. The inorganic or hybrid waveguide structures are stable, have a low light absorption loss, and have optimal refractive indices for propagating light through the waveguide combiners compared to organic resists that are not imprintable to form gratings with optimal refractive indices for propagating light through waveguides.

[0033] While the foregoing is directed to examples of the present disclosure, other and further examples of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.