Surface relief waveguide with high refractive index resist

Abstract

This disclosure describes an improved drop-on-demand, controlled volume technique for dispensing resist onto a substrate, followed by imprinting the substrate to create a patterned optical device suitable for optical applications such as augmented reality and / or mixed reality systems. The technique is capable of dispensing drops of resist at precise locations on the substrate, with precisely controlled drop volumes corresponding to an imprint template having different areas associated with different total resist volumes. Controlled drop size and placement also results in a significant reduction in residual layer thickness variation on the surface of the substrate after imprinting, compared to previously available techniques. The technique employs a resist with a refractive index closer to that of the substrate, reducing optical artifacts in the device. To ensure reliable dispensing of resists with higher refractive index and higher viscosity at smaller drop sizes, the dispensing system can continuously circulate the resist.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Patent Application No. 63 / 301,318, filed January 20, 2022, entitled “Surface Embossed Waveguide with High Refractive Index Resist,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments described herein generally relate to systems and methods for fabricating surface-embossed waveguides for eyepieces using fluids with high refractive indices, and the optical devices created thereby. Background Technology

[0004] Traditionally, resists for nanoimprint replication of waveguides or other optical components are applied by spin-coating a solvent-diluted material onto a substrate, resulting in a flat, uniform layer across the entire substrate. One advantage of this method for optical applications is the localized uniformity of the material, which can reduce scattering or phase changes of incident light due to localized roughness or height variations. However, using spin-coating for replication in manufacturing can also lead to variations in residual layer thickness. In particular, stepwise variations in residual layer thickness from one feature set to another can introduce undesirable optical artifacts, while larger residual layer thicknesses at smaller features can result in reduced image uniformity, for example, when the optical component is used as an eyepiece in augmented reality and / or mixed reality systems. Summary of the Invention

[0005] This disclosure describes methods and systems for reliably manufacturing high-quality surface-embossed waveguides for eyepieces. The optical features in the surface-embossed waveguide exhibit high nanoscale feature fidelity and high uniformity of residual layer thickness in regions where resist volume requirements may differ. Innovative aspects described in this disclosure include: i) the use of a high-refractive-index nanoimprintable resist with room-temperature viscosity and surface tension to allow control over resist volume distribution; ii) continuous recirculation of the high-refractive-index nanoimprintable fluid in a dispensing apparatus to maintain reliable resist dispensing through narrow fluid channels and nozzles; and iii) sub-2 picoliter (pL) on-demand dispensing of the high-refractive-index nanoimprintable resist to provide a thin, uniform layer whose thickness can be closely matched to an imprinting template, the different regions of which are associated with different total resist volumes on the substrate surface. In some embodiments, the substrate may include: inorganic amorphous materials (e.g., dense tantalum flint glass TADF55, quartz, etc.), crystalline materials (e.g., LiNbO3, LiTaO3, SiC, etc.), high refractive index polymers (e.g., those containing sulfur, aromatics, etc.), and / or other polymer materials (e.g., polycarbonate (PC), polyethylene terephthalate (PET), etc.).

[0006] Implementations include a system for fabricating an optical device, the system comprising: a reservoir configured to store resist; a fluid dispenser comprising a dispensing mechanism configured to dispense droplets of resist onto a substrate; a meniscus pump configured to move resist through a first channel from the reservoir to the fluid dispenser; a fluid pump configured to move undispensed resist through a second channel from the fluid dispenser to the reservoir; a fluid control device communicatively coupled to the fluid pump and the meniscus pump, the fluid control device configured to control operation of the fluid pump and the meniscus pump to maintain continuous flow of resist between the reservoir and the fluid dispenser; and a stamping mechanism operative to create the optical device by applying a stamping template to resist that has been dispensed onto the substrate, wherein applying the stamping template creates a pattern of one or more structures in the resist, and wherein the pattern corresponds to the stamping template.

[0007] In some implementations, the system further comprises a control module communicatively coupled to the fluid control device, the fluid dispenser, and the stamping mechanism. The control module can be programmed to send signals that control operation of the fluid control device, the fluid dispenser, and the stamping mechanism.

[0008] In some implementations, the volume of the droplets of resist is less than 6 picoliters, less than 4 picoliters, or less than 2 picoliters.

[0009] In some implementations, the refractive index of the resist is greater than 1.5 or 1.6 for light having a wavelength of 532 nanometers. In some implementations, the refractive index of the substrate is in a range of 1.5 to 2.7.

[0010] In some implementations, the stamping template comprises at least two regions having structures of different heights.

[0011] Implementations further include a method for fabricating an optical device, the method comprising: operating a fluid dispenser comprising a dispensing mechanism to dispense droplets of resist onto a substrate; operating a meniscus pump to move resist through a first channel from a reservoir to the fluid dispenser; operating a fluid pump to move undispensed resist through a second channel from the fluid dispenser to the reservoir, wherein the fluid pump and the meniscus pump operate to maintain continuous flow of resist between the reservoir and the fluid dispenser; and operating a stamping mechanism to create the optical device by applying a stamping template to resist that has been dispensed onto the substrate, wherein applying the stamping template creates a pattern of one or more structures in the resist, and the pattern corresponds to the stamping template.

[0012] In some implementations, the method further comprises etching at least a portion of the optical device to reduce a residual layer thickness (RLT) of the resist on the substrate, wherein etching comprises one or more of applying heat or atmospheric etching.

[0013] In some embodiments, the etching further reduces a size of at least one structure of the pattern created by applying the imprint template.

[0014] Embodiments also include a waveguide comprising: a substrate; and a plurality of structures imprinted into a volume of resist dispensed onto the substrate, wherein the resist comprises a polymer, wherein a refractive index of the resist is in a range of 1.5 to 2.1, and wherein an RLT of the resist in at least a portion of the substrate is in a range of 0 nm to 50 nm.

[0015] In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range of 0 nm to 10 nm, 40 nm to 50 nm, 30 nm to 40 nm, 20 nm to 30 nm, or 10 nm to 20 nm. In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range of 0 nm to 40 nm, 0 nm to 30 nm, 0 nm to 20 nm, or 0 nm to 10 nm. In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range of 10 nm to 40 nm or 10 nm to 30 nm. In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range of 20 nm to 40 nm.

[0016] In some embodiments, the plurality of structures provide one or more optically active regions comprising one or more of: an input coupler, a combined pupil expander, an exit pupil expander, an orthogonal pupil expander, a recycler, or an anti-reflective feature.

[0017] In some embodiments, the plurality of structures are imprinted with nano-geometries comprising one or more of: binary geometries, tilted geometries, blazed geometries, sawtooth geometries, multi-step geometries, meta-feature geometries, one-dimensional geometries, two-dimensional geometries, or three-dimensional geometries.

[0018] In some embodiments, the substrate has a refractive index in a range of 1.5 to 2.7.

[0019] In some embodiments, the plurality of structures are imprinted onto a single side of the substrate. In some embodiments, the plurality of structures are imprinted onto both sides of the substrate.

[0020] In some embodiments, sub-2 pL dispensing can be achieved by gravity without the use of a pump (e.g., without a meniscus pump, a fluidic pump, or both). One embodiment includes dispensing a droplet of resist onto a substrate, contacting the resist with a stamping template to create a pattern of one or more structures in the resist, wherein the pattern corresponds to the stamping template, polymerizing the resist to create a stamped nanostructure, and separating the stamping template from the stamped nanostructure. The resist has a refractive index in a range from 1.5 to 2.1, a residual layer thickness (RLT) of the resist in at least a portion of the substrate is in a range from 0 nm to 50 nm, and the substrate includes an inorganic material.

[0021] Embodiments of the present embodiment can have one or more of the following features.

[0022] In some embodiments, each droplet of resist has a volume less than 6 picoliters, less than 5 picoliters, less than 4 picoliters, 3 picoliters, or less than 2 picoliters. In some embodiments, each droplet of resist has a volume less than 1 picoliter.

[0023] In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range from 0 to 10 nm, 10 to 20 nm, 20 to 30 nm, 30 to 40 nm, or 40 to 50 nm. In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range from 0 to 40 nm, 0 to 30 nm, 0 to 20 nm, or 0 to 10 nm. In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range from 10 to 40 nm or 10 to 30 nm. In some embodiments, the RLT of the resist in at least a portion of the substrate is in a range from 20 to 40 nm.

[0024] In some embodiments, the substrate includes glass, LiTa03, LiNb03, SiC, or a combination thereof.

[0025] In some embodiments, the resist does not include inorganic nanoparticles. In such cases, the refractive index of the resist is typically in a range from 1.5 to 1.8.

[0026] In some embodiments, the resist includes inorganic nanoparticles (e.g., Ti02, Zr02, or both). The average diameter of the inorganic nanoparticles is typically in a range from 5 nm to 15 nm. The inorganic nanoparticles can comprise about 10 vol% to about 60 vol% of the resist. The refractive index of the resist is typically in a range from 1.5 to 2.1.

[0027] In some embodiments, the viscosity of the resist is in a range from 5 to 25 centipoise (cP) at 25 °C.

[0028] In some implementations, the surface tension of the resist is in a range of 20 to 60 millinewtons (mN) per meter (m) at 25 °C.

[0029] In some implementations, dispensing the droplet of resist includes pumping the resist from the reservoir to the fluid dispenser through a first channel. Some implementations include maintaining a continuous flow of resist between the reservoir and the fluid dispenser. In some implementations, maintaining a continuous flow of resist between the reservoir and the fluid dispenser includes pumping un-dispensed resist from the fluid dispenser to the reservoir through a second channel.

[0030] In some implementations, dispensing the droplet does not require pumping of the resist (e.g., does not require use of a meniscus pump, a fluid pump, or both to pump the resist).

[0031] Other features and advantages of the present application will be apparent from the following detailed description, and from the drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 An example system of fluid dispensing and imprinting is shown in accordance with implementations of the present disclosure.

[0033] Figure 2 A flowchart of an example manufacturing process in accordance with implementations of the present disclosure is depicted.

[0034] Figure 3 Example results of different imprinting processes are depicted.

[0035] Figures 4A-4C Example imprinted nanostructures in accordance with implementations of the present disclosure are depicted.

[0036] Figures 5A-5N Images of various example nanostructure geometries in accordance with implementations of the present disclosure are shown.

[0037] Figure 6A And Figure 6B An example eyepiece design in accordance with implementations of the present disclosure is depicted.

[0038] Figures 7A-7E Images of simulated test results of waveguides manufactured using various techniques are shown. DETAILED DESCRIPTION

[0039] The implementations described herein provide a drop-on-demand, controlled volume dispensing technique for dispensing fluid onto a substrate and precisely controlling the volume of the dispensed drops and the location of the dispensed drops on the substrate. The dispensed fluid can then be imprinted to create a patterned optical device suitable for augmented reality (AR) and / or mixed reality (MR) systems and / or other suitable optical applications. The innovative techniques described herein are capable of dispensing drops of dispensed fluid (which can also be described as resist, photoresist, or resin) that are smaller in size than the drop sizes used in previously available drop-on-demand jetting techniques. In particular, the implementations employ drop sizes that are less than two picoliters (pL), which provides for the dispensing of thin and uniform layers of resist that can target volumes that can match different regions of an imprint template that are associated with different total resist volumes suitable for filling the template. The use of smaller drop sizes also results in a significant reduction in interconnect residual layer thickness (RLT) variation across the surface of the substrate compared to previously available techniques that employ larger drop sizes. In addition, the techniques described herein employ dispensed resist that has a high refractive index that can more closely match the refractive index of the substrate, thereby reducing optical artifacts in the manufactured optical device. The viscosity of the resist with a high refractive index can also be higher than the resists used in previously available techniques. Accordingly, to ensure reliable dispensing of the higher viscosity resist with smaller drop sizes, the implementations employ a resist dispensing system that provides for substantially continuous recirculation of the resist fluid. This recirculation enables the system to operate the fluid at room temperature viscosities and surface tensions while maintaining reliable dispensing through narrow fluid passages and nozzles, thereby facilitating high yield manufacturing of high quality optical devices.

[0040] High refractive index materials are often used as substrate materials for surface-relief based diffractive waveguides in AR and / or MR systems. The use of high refractive index substrates helps support a wide field of view for virtual images that can be coupled into and out of the waveguide to the user’s eye. However, surface-relief diffractive features are often composed of materials with a lower refractive index (e.g., less than 1.6) than the substrate. This refractive index mismatch can result in poor optical artifacts and limit image brightness and overall uniformity, including the user-to-world ratio of image brightness, when used as optical combiners in AR / MR systems. In one example, for a single-sided design with surface features on one side of the substrate, the user-to-world ratio can increase from 1 : 1 to 1.25: 1 as the resist refractive index increases from 1.53 to 1.65. As provided by the implementations described herein, the use of a resist with a higher refractive index allows for the use of gratings with higher diffraction efficiency compared to similar gratings using the same nanogeometry, thereby allowing for higher values of image brightness and uniformity at the desired eye box location or range.

[0041] Changes in RLT and / or RLT uniformity that are larger (e.g., produced using conventional techniques) can also result in optical artifacts. Accordingly, the embodiments described herein also provide higher quality optical devices by using smaller resist droplet sizes during resist dispensing, resulting in less overall change in RLT uniformity and less variation between regions of different feature heights, if desired. The embodiments described herein provide a system and method of manufacturing high quality optical devices that allow for the use of high refractive index resist materials to minimize the difference between the refractive index of the resist and the substrate, thereby reducing the adverse effects caused by the refractive index difference. The embodiments also provide for the manufacture of devices with thin and / or uniform RLT to meet cost and yield considerations for high volume manufacturing of optical devices.

[0042] As used herein, optically transparent generally refers to the physical property of allowing light to pass through a material without being scattered or absorbed. As used herein, high refractive index generally refers to a refractive index (n) (e.g., of an imprint polymer resist) that is greater than 1.5, or greater than 1.6 or 1.7. In one example, high refractive index refers to n that is greater than 1.6 or 1.7 and less than 1.9. In one example, high refractive index refers to n that is in the range of 1.5 to 1.8.

[0043] As used herein, total thickness variation (TTV) refers to the difference between the maximum and minimum values of the substrate thickness in a series of point measurements across the entire dimensions of the substrate. For a substrate having a patterned surface, TTV refers to an approximation evaluated by ignoring the contribution of the pattern features to the thickness. For example, the thickness (or height) of a typical feature on a patterned substrate can range from about 10 nanometers (nm) to 150 nm. This thickness is determined at least in part by the trench depth of the template, which can vary by 10% (e.g., 1 nm to 15 nm). The TTV of an unpatterned substrate typically exceeds 100 nm, and sometimes is in the micrometer range. Thus, the additional thickness variation introduced by the pattern features of a patterned substrate can be negligible and can be ignored as an approximation. Accordingly, the thickness of a patterned substrate evaluated at a location including a protrusion can be approximated by subtracting a given feature thickness from the evaluated thickness to arrive at an adjusted thickness, while the thickness of a patterned substrate evaluated at a location without a protrusion remains unchanged. That is, the adjusted (e.g., reduced) thickness of a feature area and the native thickness of an unpatterned area can be used to calculate the TTV of a substrate having a patterned surface. The low TTV values described herein result at least in part from a flat, optical grade glass substrate that is polished to meet the required flatness, and the methods described herein to minimize or reduce uneven material shrinkage during curing. Low TTV can also be imparted to inorganic material substrates by extrusion. Low TTV can also be imparted to polymer substrate materials and achieved from the mold surface when such substrates are molded (e.g., injection molded, ultraviolet (UV) or heat molded, extruded, etc.), such substrates composed of high refractive index polymers (e.g., containing sulfur, aromatic, etc.) and other polymer materials (e.g., polycarbonate (PC), polyethylene terephthalate (PET), etc.).

[0044] Figure 1 is a system diagram illustrating an example system 100 for dispensing a fluid (e.g., a high refractive index nanoimprint resist) onto a substrate and imprinting the dispensed fluid to create a pattern on the substrate.

[0045] As Figure 1As shown, the system 100 can include a substrate 102 supported by a platform 104. The substrate 102 can be composed of any suitable material, such as glass or a polymer. The platform 104 can be configured to support the substrate 102 and stabilize the substrate 102 during fluid dispensing, imprinting, curing, etching, and / or other manufacturing operations. A fluid dispenser 106 is configured to dispense droplets (or drops) of a fluid 120 (e.g., resist) onto the substrate 102. The fluid dispenser 106 can also be described as one or more print heads. The fluid 120 is held in a reservoir 108, which is connected to the fluid dispenser 106 by one or more channels (e.g., tubes, conduits, etc.) of a suitable type, material, and size. A fluid pump 110 operates to circulate the fluid 120 between the reservoir 108 and the fluid dispenser 106. A meniscus pump 112 operates to extract drops of the fluid 120 from the reservoir 108, which flow from the reservoir 108 to the fluid dispenser 106.

[0046] A fluid controller 114 is communicatively coupled to the pumps 110 and 112 and sends signals to the pumps 110 and 112 to control their operation and maintain continuous circulation flow of the fluid 120 within the system. As described herein, the continuous circulation flow of the fluid 120 enables reliable dispensing of high refractive index, high viscosity fluids with drop sizes that are smaller than conventional techniques. The system 100 can include one or more pressure sensors 116 for measuring the pressure of the fluid 120 as it circulates within the system. Although Figure 1 An example is depicted using two pressure sensors 116(1) and 116(2), but the system can include any suitable number and type of pressure sensors 116 at any suitable location in the system. The fluid controller 114 is communicatively coupled to the pressure sensors 116 and can receive pressure data from the pressure sensors 116 describing the pressure of the fluid 120 at one or more locations in the system. The fluid controller 114 can use the pressure data to control the circulation flow of the fluid 120 in the system and ensure substantially continuous circulation (e.g., recirculation) flow.

[0047] In the system 100, fluid recirculation through the print head can be maintained by combining a diaphragm fluid pump that supplies fluid to the inlet of the print head at positive pressure with a meniscus vacuum pump that applies negative pressure to the outlet of the print head. Alternatively, a second diaphragm fluid pump can be used to apply negative pressure to the outlet. By applying appropriate inlet and outlet pressures, the meniscus pressure at the print head nozzles and the pressure differential through the print head can be independently controlled. The meniscus pressure setpoint is chosen to prevent fluid from dripping from the print head nozzles and air from entering the print head through the nozzles. The pressure can be set in a range between -10 and -40 mbar. The pressure differential is proportional to the resist flow rate through the print head and is set to deliver a flow rate of between approximately 50 and 150 milliliters (mL) per minute.

[0048] To ensure system reliability, various hardware elements of the system can be designed with specific resist compositions in mind for the system's internal circulation. The composition of system components that interact with the resist can be critical, as some weaker polymer compositions can begin to chemically dissolve over time and mix with the resist fluid. Thus, more chemically resistant parts (e.g., made of polytetrafluoroethylene (PTFE), nylon, etc.) can be used to ensure reliable operation of the printhead system, including components involved in fluid recirculation.

[0049] The control module 118 is communicatively coupled to the fluid controller 114 and the fluid dispenser 106 to control their operation. In some implementations, the control module 118 is a computing device that includes at least one processor and a memory. The memory can store a computer program that includes instructions that, when executed by the at least one processor, cause the processor to perform operations to control the fluid controller 114, the fluid dispenser 106, and / or other components of the system. The control module 118 can be any suitable type of computing device, such as a personal computer, and can communicate with other computing devices to receive instructions, provide data, etc.

[0050] In some implementations, the system 100 includes a mechanism (not shown) that moves the platform 104 and the substrate 102 along the platform travel direction 122 between multiple stages of a process of manufacturing the optical device. The mechanism can also be controlled by the control module 118. The platform 104 (and the substrate 102) can be moved from a first position at which the fluid 120 is dispensed onto the substrate 102 during a first stage of the manufacturing process to a second position. At the second position, the substrate 102 is imprinted during a second stage using an imprint template 124 that forms the fluid 120 into a desired pattern to create the optical device. The imprint template 124 can be operated by an imprint mechanism 126 that can be controlled by the control module 118. During one of the stages or in a separate stage, the fluid 120 can also be cured using light (e.g., UV light), heat, and / or a combination of light and heat. Alternatively, the system can be configured such that the dispensing, imprinting, and / or curing of the fluid 120 are performed at the same position of the platform 104.

[0051] Although Figure 1An example of a system 100 including a single fluid dispenser 106 is shown, but other implementations are possible. The system can be a single fluid circulation system that includes multiple fluid dispensers to dispense resist to different substrates and / or different portions of a substrate in parallel to enable more efficient and higher capacity manufacturing. Further, the system can include multiple fluid circulation systems to circulate different resist fluids (e.g., having different refractive indices) and dispense different resists to different areas of a substrate through different print heads. For example, a first resist having a first refractive index can be dispensed to a combined pupil expander (CPE) area of a substrate, while a second resist having a second refractive index can be dispensed (e.g., in parallel with the first resist) to a different area, such as an in-coupling grating (ICG) or recycler. Thus, manufacturing can include a single dispensing and imprinting step that dispenses and imprints multiple resists in different areas. Alternatively, multiple systems can circulate and dispense the same fluid to enable higher throughput in the manufacturing process.

[0052] Conventional systems employ spin-coating techniques to apply resist to a substrate. In such systems, the application of nanoimprint replicated resist for waveguides or other optical elements is achieved by spin-coating a solvent-diluted material onto a substrate, thereby forming a uniform, planar layer across the substrate. This conventional approach has the advantage that it is an industrially mature process, and it provides excellent local uniformity of dispensed material. This uniformity minimizes scattering or phase changes of incident light due to local roughness or height variations. However, there are disadvantages to manufacturing replication using conventional spin-coating techniques. If the goal is to create non-uniform target features (e.g., having different heights and / or duty cycles), the amount of resist needed to fill the template features during nanoimprinting will vary. Since the underlying applied film is initially distributed substantially uniformly, spin-coating can result in a final film (e.g., after template imprinting) having varying RLTs, as shown. Large step changes in RLT from one set of features to another can introduce unwanted optical artifacts. Larger RLTs under smaller features can result in reduced image uniformity, especially on the temple side. Another manufacturing disadvantage of spin-coating is that more than 95% of the resist solution is wasted, thereby significantly increasing manufacturing costs. Figure 3

[0053] ​Unlike spin coating, embodiments employ a modified drop-on-demand jetting and flash imprint lithography (J-FIL) process to apply the resist for nanoimprinting. The J-FIL process locally adjusts the amount of fluid to fit the features, reducing the large step changes in RLT from one feature area to another compared to the step changes caused by spin coating. Traditional J-FIL processes use dispensing materials in large droplets (e.g., > 3 pL) with a refractive index greater than 1.6 and produced by standard industrial printheads. However, traditional J-FIL processes have drawbacks. With this process, the droplets of resist do not spread to form a uniform local film, thus introducing some local non-uniformity in the thickness of the imprint fluid at the droplet merge. In addition, due to the digital nature of the traditional J-FIL dispensing process, not all target thicknesses or boundaries can be perfectly matched.

[0054] The embodiments described herein provide a system and method that is an improvement over traditional J-FIL technology that addresses the problems of traditional J-FIL technology. The embodiments employ a high refractive index resist in smaller (e.g., < 2 pL) droplets with higher resolution to improve local flatness and further reduce the step height variation in RLT in areas of similar nano-features (also referred to as features, structures, or nanostructures) and in transitions between two or more feature areas in an imprint pattern. In other words, the embodiments employ a high refractive index resist in smaller droplets to improve local surface flatness (RLTu) and reduce the magnitude of RLT step changes at boundaries and / or area transition regions.

[0055] To achieve sub-2 pL nanoimprinting with a high refractive index resist, the techniques described herein employ the following combination: 1) a high refractive index (e.g., n > 1.6) fluid with rheological properties compatible with a controlled volume dispensing process; 2) fluid recirculation to maintain reliable jetting in the printhead of the fluid dispenser 106 (e.g., printhead) that dispenses the resist; 3) a multi-nozzle fluid dispenser 106 capable of producing sub-2 pL droplets of resist and delivering them to a substrate with sufficient precision to provide a nanoimprinted optical device with minimal defects.

[0056] To be able to be dispensed by a jetting dispensing process, the material must typically have a viscosity in the range of 5 to 25 centipoise (cP) and a surface tension in the range of 20 to 60 (e.g., 20 to 40) millinewtons (mN) per meter (m). Many high refractive index ingredients, whether organic or inorganic, have properties that fall outside of this range. In traditional jetting applications, heating is used to reduce the viscosity of a more viscous material to a jettable viscosity range. However, heating can present risks of oxidation and gelation, and is generally not suitable for reactive materials designed to be UV cured. Accordingly, embodiments employ high refractive index resists that have a higher refractive index than competing commercial materials, while having rheological properties that allow for jetting dispensing at room temperature.

[0057] Embodiments support the use of various suitable types of high refractive index resists. In some embodiments, the resist (e.g., fluid 120) is a polymer-based resin to which nanoparticles (NPs) of a higher refractive index material are added. Alternatively, the resist can be a polymer-based resin without the incorporation of NPs. The addition of NPs can increase the overall refractive index of the material, which is beneficial to more closely match the refractive index of the substrates described herein. However, the addition of NPs can also cause Rayleigh scattering of light in the resist. Accordingly, the selection of a resist that includes NPs or omits NPs can be based on balancing considerations, such as higher refractive index versus more scattering. For example, a resist with a refractive index of 1.6 or 1.7 and without NPs can provide optimal performance, providing a higher refractive index (e.g., closer to the refractive index of the substrate) while avoiding scattering caused by the presence of NPs.

[0058] Organic (meth)acrylate monomers and oligomers typically have a refractive index of about 1.5 at a wavelength of 532 nm. Both sulfur atoms and aromatic groups have a higher polarizability that can be added to these acrylate ingredients to increase the refractive index of the formulation. This effect can be limited due to the fluid viscosity limitations of the jetting process being less than 20 to 25 cP, as well as the upper limit on the refractive index of sulfur-containing molecules. This approach can produce jettable and imprintable resists with a refractive index as high as 1.72 at a wavelength of 532 nm.

[0059] The addition of inorganic nanoparticles (NPs) such as Zr02 and Ti02 can further significantly increase the refractive index. Pure Zr02 and Ti02 crystals can reach a refractive index of 2.2 and 2.4-2.6 at 532 nm, respectively. For the preparation of optical nanocomposites of acrylate monomers and inorganic nanoparticles, the particle size is less than 10 nm to avoid excessive Rayleigh scattering. Zr02 NPs tend to agglomerate in the polymer matrix due to their high specific surface area, high polarity, and incompatibility with the cross-linked polymer matrix. Surface modification of the NPs can be used to overcome this problem. In this technique, the hydrophilic surface of Zr02 is modified to be compatible with organic materials, enabling uniform mixing of the NPs with the polymer. This modification can be done using a capping agent containing silane and carboxylic acid. One end of the capping agent is bonded to the Zr02 surface; the other end either contains a functional group that can participate in acrylate cross-linking or a non-functional organic moiety. Examples of surface-modified sub-10 nanometer Zr02 particles include Pixelligent Technologies TM and Cerion Advanced Materials TM offer particles. These functional nanoparticles are typically sold as a uniform suspension in a solvent in the form of a uniform mixture that can be combined with other base materials to produce a resist formulation with a jettable viscosity and increased refractive index.

[0060] The higher surface tension of some high refractive index components can pose a challenge to the implementation of a jet-based nanoimprint lithography (NIL) process. High surface tension tends to support the formation of bubbles in the fluid. Bubble formation and subsequent air blockage of the nozzles and fluid channels are common reliability issues for jetting processes. This problem becomes more severe as the channel and nozzle size is reduced to support the formation of smaller droplets, such as those used in the techniques described herein. Accordingly, the implementations described herein provide systems and methods that include a continuous circulation of resist fluid. The continuous flow of fluid through the channels in the system 100 clears bubbles from the narrow channels and maintains a steady supply of fluid.

[0061] This approach is also applicable to the addition of resist solutions containing higher vapor pressure solvents (e.g., high refractive index inorganic nanoparticles dispersed in a solvent) to the resist formulation. Without recirculation, solvent evaporation at the faceplate of the fluid dispenser 106 can lead to increased viscosity and nozzle failure. This in turn can have a negative impact on the quality of the imprint, the RLTu, and the fidelity of the nanofeatures, and can severely impact the image quality of the manufactured eyepiece waveguide, including image sharpness, contrast, uniformity, and efficiency.

[0062] Droplet formation and accurate placement are particularly important for dispensing of high viscosity and high surface tension fluids. High viscosity and high surface tension negatively impact the NIL process by slowing feature filling and droplet pre-spread, respectively. Lower refractive index materials are generally easier to spread and fill and are less likely to produce RLT changes. Furthermore, higher refractive index imprint layers (e.g., n > 1.6) are more optically sensitive to RLT changes than imprints of lower refractive index resists (e.g., n = 1.53). For nanoparticle containing resist formulations, long time delays before droplet coalescence can cause material phase separation and undesirable changes in the refractive index of the applied resist. Smaller droplets with smaller inter-droplet gap spacing have a greater advantage when using high refractive index materials because smaller droplets can be placed more accurately and densely on the substrate, mitigating the issues of slow droplet pre-spread and slow feature filling that can arise when using high refractive index fluids with high viscosity and high surface tension. Thus, by modifying the traditional J-FIL process with the use of high refractive index materials, smaller droplet sizes, and reliable operation through fluid recirculation, implementations allow for the fabrication of high performance optical components. With reference to Figure 3 Advantages provided by implementations described herein are further described.

[0063] Figure 2 is a flowchart illustrating an example process 200 of fabricating an optical device according to implementations described herein. At 202, a droplet of resist is dispensed onto a substrate using a fluid dispenser. As described herein, the fluid dispenser (also referred to as a print head) can be configured to dispense droplets using a controlled volume dispensing mechanism of Figure 1 At 204, a meniscus pump is used to move resist from a reservoir through a first channel to the fluid dispenser. At 206, the fluid pump is operated to move resist (e.g., un-dispensed excess resist) from the fluid dispenser back to the reservoir through a second channel. At 208, an imprint mechanism is operated to apply an imprint template to the resist on the substrate to generate an optical device (e.g., an imprinted substrate to be used as a waveguide). The process can also include steps to cure the resist using ultraviolet light and / or heat, as described herein.

[0064] In some implementations, one or more additional steps can be performed at 210 to further reduce the RLT, thereby creating an optical device (e.g., a waveguide) with an ultra-thin RLT. For example, an appropriate etching process can be performed to further reduce the RLT. For example, after the resist is dispensed and the template is applied (in some implementations, cured), the etching can reduce the RLT from an initial level (50 nm or below) to an RLT in the range of about 0 to 10 nm. This RLT reduction can be done across the substrate surface or a particular region (e.g., at least a portion of the eye pupil expander (EPE) region of the waveguide). In some examples, the etching can employ a template or other type of mask to control which areas are etched to reduce the RLT.

[0065] In some implementations, the RLT in one or more regions of the substrate can be reduced by applying heat. For example, heat in the range of 120 to 200 degrees Celsius (C) can be applied to the substrate and / or the imprinted pattern to reduce the RLT. This heat application can also reduce the size of the imprinted nano-features. The applied heat can reduce the RLT and / or the nano-features by causing thermal shrinkage of the cross-linked polymer chains. For example, if the desired nano-geometry includes features with a height of 20 nm (e.g., relative to the RLT), the dispensing and imprinting can be configured to create taller features, which are then reduced to the desired height by applying heat. Similarly, if the desired final RLT is lower than 10 nm, an initial RLT of 20 nm can be reduced to the desired RLT by applying heat. Similarly, we can start with an imprint of 30 nm and end up with an imprint of sub-10 nm, in some cases, close to 0 nm, after the post-heat treatment.

[0066] In some implementations, atmospheric plasma etching (e.g., using a plasma of an argon and O2 mixture) can reduce the RLT to 0 nm as needed, thereby providing a free-standing nanostructure on the substrate. This solution can be employed in cases where the template can have a pre-defined biased imprint geometry, which takes into account the isotropic etch loss of the feature width when the RLT is removed. Using atmospheric plasma at relatively low temperatures, such as temperatures below 60 °C, can also smoothly reduce the nano-geometry features. Ar +The presence of ions and O radicals can physically and / or chemically isotropically remove the organic material. In some embodiments, UV O3 treatment at atmospheric pressure and temperatures below 50 °C can also reduce the imprinted nano-geometries and RLT on such substrates. In this example, oxygen radicals generated from O3 in the presence of UV light tend to react and isotropically remove the organic material. In some embodiments, reactive ion etching at pressures lower than atmospheric pressure can also be used to achieve a more anisotropic etch in the presence of a mixture of one or more of Ar, O2, N2, He, and CF4.

[0067] In some cases, one or more operations in process 200 are replaced or combined with another operation, the order of one or more operations is interchanged, two or more operations occur simultaneously or in succession, or any combination thereof. In some cases, process 200 can include one or more additional operations described herein.

[0068] Figure 3 A graph 300 showing example results of three different imprint processes is provided. As described above, after resist is dispensed onto a substrate 102, an imprint template 124 is applied to the resist (e.g., fluid 120) to imprint a pattern onto the substrate 102. In this particular example, the template 124 includes three regions 302(1), 302(2), and 302(3) that include features of different heights, 90 nm, 60 nm, and 30 nm, respectively. It should be noted that, Figure 3 The particular dimensions and other values shown in FIG. 300 are examples, and embodiments are not limited to these examples. The goal of the imprint process is to imprint a pattern onto the substrate 102 that most accurately reflects the template 124 using the template 124. In this example, the goal is to create a pattern on the substrate 102 that includes three respective regions 304(1), 304(2), and 304(3) having corresponding height differences, and minimal RLT variation. Figure 3 The particular template 124 shown in FIG. 300 is an example, and embodiments are not limited to this example.

[0069] Embodiments can employ any suitable template that imprints any suitable pattern onto the substrate 102. Furthermore, although the substrate 102 depicted in the present example is 350 pm glass with a refractive index of 2.0, embodiments can employ any suitable size and material of substrate. For example, the substrate 102 can be composed of a polymeric material rather than glass.

[0070] Figure 3Three example results 306, 308, and 310 resulting from three different imprinting techniques are shown. In the first example 306, spin coating is used. In this example, a uniform 100 nm spin-coated resist is paired with an example template having three different feature height regions, which can be found in diffractive optical elements. Due to the drawbacks of the spin coating technique as described above, this process results in a 15 nm step change in RLT height between the feature regions 304. The second example 308 shows the results using a traditional J-FIL technique. Using this process, the fluid volume can be locally varied to match the feature requirements, reducing but not eliminating the RLT step change between regions. As described above, the large droplet size used in traditional J-FIL still results in local thickness inconsistencies, which can lead to RLT variations between regions.

[0071] The third example 310 shows the results using an improved J-FIL technique according to the embodiments described herein. Since the embodiments are able to use smaller droplets with a smaller pitch, the local fluid density and boundaries can be controlled more effectively, greatly mitigating or eliminating the RLT variations between regions, and also enabling smaller overall RLT, as shown. Smaller pitch corresponds to a reduction in the gap size between droplets. The advantage of using smaller droplet sizes is that the packing density of the droplets can be increased while still maintaining the required total volume of dispensed resist. Smaller and more densely packed droplets can provide better RLT uniformity in both the nano-feature regions as well as the blank regions without features.

[0072] The techniques described herein enable high refractive index resists to be dispensed and imprinted on a substrate, providing very low RLT compared to previously available solutions. For example, the embodiments described herein can provide RLTs of less than 30 nm, or even less than 15 nm. This can be achieved because the dispensing mechanism is able to dispense droplets of resist onto the substrate in locations where resist is needed according to the template being used for imprinting. In other words, the mechanism enables more precise control of the placement of resist on the substrate in terms of both space and volume, such that more resist is placed in locations where the template is creating larger structures, which can require larger volumes of resist, for example, in order to more optimally fill the template during imprinting. The techniques described herein are also able to imprint more complex or more precise structures compared to structures that can be created using previously available methods, because the dispensing mechanism is able to place droplets precisely in locations corresponding to the structures to be created by the template compared to traditional (e.g., spin coating) techniques, which apply a substantially uniform layer of fluid over a region of the substrate. This dispensing mechanism provides flexibility for imprinting more complex features to achieve the required optical effects in a waveguide, and provides more control over the specific RLTs that can be imparted to different regions of the substrate.

[0073] In some examples, the diffractive surface relief imprint is fabricated on a substrate composed of high refractive index resist polymers with ultra-thin RLTs in the range of 0 nm to 50 nm. In some implementations where imprinting is performed to manufacture waveguides for optical devices such as AR / MR devices, RLTs of 10 to 20 nm can be used for various portions of the waveguide, e.g., input coupling region, combiner pupil expander, exit pupil, orthogonal pupil expander, recycler, anti-reflective features, etc. In each of the graded regions of the waveguide eyepiece, high refractive index ultra-thin RLT imprints on the waveguide substrate can provide the required nanometer feature grading in duty cycle and / or feature height.

[0074] High refractive index ultra-thin imprints can be performed on substrates to create nanometer geometries in various configurations. For example, the nanometer geometries can include the following features: binary (e.g., rectangular), slanted, blazed, sawtooth, multi-step, and / or more complex meta-features, etc. These features can include one-dimensional lines and spaces, two-dimensional features (e.g., symmetric posts or holes), alternating gratings or two-dimensional features with same or different pitches, and / or three-dimensional features (e.g., asymmetric posts or holes).

[0075] Figures 4A-4C Example imprinted nanometer structures are depicted, such as triangular or sawtooth structures 410, trapezoidal structures 420, and diamond structures 430, respectively, in accordance with implementations of the present disclosure. Other suitable types of nanometer structures can also be created. Figures 5A-5N Captured images of various geometries created using the techniques described herein are shown. For example, Figures 5A-5F The scale bar is 100 nanometers. Figures 5A-5E Rectangular gratings of various sizes and pitches are shown. Figure 5F Sawtooth gratings are shown. Figure 5G Multi-step gratings are shown. Figure 5H Sawtooth gratings are shown. Figure 5I Slanted gratings are shown. Figure 5J Multi-level embedded features are shown. Figure 5K Two-dimensional structures are shown. Figure 5L Three-dimensional structures with two sets of grating stacks are shown. Figure 5M Three-dimensional structures with lines and holes are shown. Figure 5N Three-dimensional blazed grating arrays are shown.

[0076] In some examples, the refractive index resist has a refractive index of about 1.5 to 2.1 and is imprinted on a substrate having a refractive index of about 1.5 to 2.7 to create a surface-relief diffractive waveguide. The high refractive index resist dispensed on-demand is used to imprint in different regions with controlled RLT (e.g., in the range of 5 nm to 1000 nm) and / or to provide RLT modulation on the waveguide surface to change the way light propagates through the eyepiece. In one example, different RLTs can be used to create different regions, such as a first RLT region (e.g., RLT < 30 nm) at a first grating height in the CPE optical path, a second RLT region (e.g., RLT > 40 nm) at a second grating height, and a third RLT region (e.g., RLT < 30 nm) on the rest of the CPE grating height region, such that the second region is between the first and third regions. Imprinting can be performed on one or both sides of the substrate and can be performed on any suitable substrate form, such as a wafer, a film, a sheet, and the like.

[0077] As described herein, the imprinting techniques described herein can be used to manufacture waveguides for eyepieces or other suitable optical devices for AR / MR devices. Figure 6A and 6B An example eyepiece design with example dimensions is depicted in accordance with embodiments of the present disclosure. Figure 6A is a schematic diagram 600 of the world side (e.g., outward-facing side) of an example eyepiece design. Figure 6B is a schematic diagram 650 of the eye side (e.g., inward-facing side) of an example eyepiece design. The scale values on the horizontal and vertical axes are in millimeters (mm).

[0078] Referring to Figure 6AThe bottom 602 of the example eyepiece design is a CPE region that combines the functions of an optical pupil expander (OPE) and an EPE. The top 604 of the design is a recycler region that includes gratings that send light that would otherwise escape from the eyepiece or be absorbed at the edge of the eyepiece back into the eyepiece. In this example, the diameter of the eyepiece is 36.3 mm. On the left side 606 of the eyepiece, the grating depth is 90 nm. On the right side 608 of the eyepiece, the grating depth is 15 nm. The middle region 610 includes a plurality of regions that have a grating depth that decreases from 90 nm on the left to 15 nm on the right. Each region can include thousands of grating lines, and each grating line can be approximately 200 nm in width. Each region can have a substantially uniform grating depth across the region. In some examples, the grating depth corresponds to the height of the features, and is measured from the top of the feature to its bottom, with a substantially uniform RLT in the various regions and / or domains. Alternatively, the RLT can be different in different regions or domains. The regions are 1 mm in width, and are tilted at an angle of -30 degrees relative to the vertical. The gratings in these regions are square ridge cross-sections that are tilted at -60 degrees relative to the vertical. Region 612 includes a plurality of pie-slice regions. These regions are anti-reflective structures. One of these regions can include an ICG 614 that is approximately 33 mm from the center of the CPE, as shown in the illustrated example.

[0079] For Figure 6B The illustrated eye-side view can employ the same dimensions as described in Figure 6A The grating groove direction is +60 degrees, and the depth taper direction is tilted at +30 degrees relative to the vertical.

[0080] In some implementations, different grating patterns can be used in different regions. For example, an ICG region can include triangular features in its grating pattern, while a CPE region can include features that are binary (e.g., rectangular) in shape in its grating pattern. Different patterns can be employed as desired to provide different optical effects.

[0081] In this example configuration of the eyepiece, a projector that inputs graphics into the eyepiece can be located on the right side of the diagram, corresponding to the location of the ICG. Thus, the light input by the projector can propagate through the waveguide to the left, and be output to the user’s eye at various points in the CPE region. The grating depth can increase as the distance from the projector increases, to provide greater outcoupling power as the distance from the projector increases. Given that the propagating light can be attenuated as it travels through the waveguide, the greater the grating depth the farther away from the projector, can result in a more uniform outcoupling of light on the surface of the eyepiece overall.

[0082] Figures 7A-7EImages showing simulated test results of waveguides manufactured using various techniques are shown. The simulations performed show how different types of waveguides propagate an input image that is uniform across the entire field of view of the display well. The simulations model the same grating pattern for all five results, and the variable that is changed is the RLT. Figure 7A Image 710 in FIG. 7 shows simulated test results of a waveguide manufactured according to the innovative techniques described herein to provide a constant and small RLT across the entire area of the waveguide. As shown, the result of a constant and small (e.g., about 20 nm) RLT is that the resulting image is best delivered to the eye of a user of the optical system, e.g., given an input image that is uniform across the field of view, the result here is a substantially reproduced uniform input test image. The simulation can yield an eye box energy (EBE) fraction, which describes what percentage of the energy of the input image ends up being delivered to the eye box (the area occupied by the eye). The EBE fraction for 710 is 7.91%. The simulation can also yield a low frequency 80 / 20 (LF 8020) fraction, which is 80% luminance minus 20% luminance, divided by 50% luminance. Ideally, this fraction should be zero. The LF 8020 fraction for 710 is 1.32.

[0083] Figures 7B-7E Images showing simulated results of previously available methods (e.g., spin-on dispensing methods) that can only apply a constant volume of resist on the substrate surface, thus requiring a larger volume of resist to be dispensed to ensure the template is completely filled. Thus, these traditional methods produce a product with a thicker and / or more non-uniform RLT compared to the innovative techniques described herein. Figure 7B Image 720 in FIG. 7 shows the results of applying a constant volume of resist with a minimum RLT of 20 nm. The EBE fraction for this simulation is 7.39% and the LF 8020 fraction is 1.70. Figure 7C Image 730 in FIG. 7 shows the results of applying a constant volume of resist with a minimum RLT of 30 nm. The EBE fraction for this simulation is 7.2% and the LF 8020 fraction is 1.77. Figure 7D Image 740 in FIG. 7 shows the results of applying a constant volume of resist with a minimum RLT of 40 nm. The EBE fraction for this simulation is 6.87% and the LF 8020 fraction is 1.956. Figure 7E Image 750 in FIG. 7 shows the results of applying resist with a RLT of 200 nm. As shown in the output image, the results using the innovative techniques described herein are more uniform compared to other more traditional methods. It is worth noting that the simulation here is performed using a more traditional method assuming RLTs of 20, 30, and 40 nm. This is far below the typical values for currently used industry standard techniques, which tend to produce RLTs of 100 to 200 nm.

[0084] In some embodiments, sub-2pL dispensing can be achieved by gravity without the use of a pump. One embodiment includes dispensing a droplet of resist onto a substrate, contacting the resist with a stamping template to create a pattern of one or more structures in the resist, wherein the pattern corresponds to the stamping template, polymerizing the resist to create a stamped nanostructure, and separating the stamping template from the stamped nanostructure. The resist has a refractive index in the range of 1.5 to 2.1, a residual layer thickness (RLT) of the resist in at least a portion of the substrate is in the range of 0 nm to 50 nm, and the substrate is composed of an inorganic material.

[0085] Implementations of the present embodiment can have one or more of the following features.

[0086] In some implementations, the volume of each droplet of resist is less than 6 picoliters, less than 5 picoliters, less than 4 picoliters, 3 picoliters, or less than 2 picoliters. In some implementations, the volume of each droplet of resist is less than 1 picoliter.

[0087] In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0 to 10 nm, 10 to 20 nm, 20 to 30 nm, 30 to 40 nm, or 40 to 50 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 0 to 40 nm, 0 to 30 nm, 0 to 20 nm, or 0 to 10 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 10 to 40 nm or 10 to 30 nm. In some implementations, the RLT of the resist in at least a portion of the substrate is in the range of 20 to 40 nm.

[0088] In some embodiments, the substrate includes glass, LiTa03, LiNb03, SiC, or a combination thereof.

[0089] In some implementations, the resist does not contain inorganic nanoparticles. In this case, the refractive index of the resist is typically in the range of 1.5 to 1.8.

[0090] In some implementations, the resist includes inorganic nanoparticles (e.g., Ti02, Zr02, or both). The average diameter of the inorganic nanoparticles is typically in the range of 5 nm to 15 nm. The inorganic nanoparticles can comprise about 10 vol% to about 60 vol% of the resist. The refractive index of the resist is typically in the range of 1.5 to 2.1.

[0091] In some implementations, the viscosity of the resist is in the range of 5 to 25 centipoise (cP) at 25 °C.

[0092] In some implementations, the surface tension of the resist is in the range of 20 to 60 millinewtons (mN) per meter (m) at 25 °C.

[0093] In some embodiments, dispensing a droplet of resist includes pumping resist from a reservoir to a fluid dispenser through a first channel. Some embodiments include maintaining a continuous flow of resist between the reservoir and the fluid dispenser. In some embodiments, maintaining a continuous flow of resist between the reservoir and the fluid dispenser includes pumping un-dispensed resist from the fluid dispenser to the reservoir through a second channel.

[0094] Embodiments of the present disclosure

[0095] Example 1 is a system for fabricating an optical device, the system comprising:

[0096] a reservoir configured to store a resist;

[0097] a fluid dispenser including a dispensing mechanism configured to dispense a droplet of the resist onto a substrate;

[0098] a meniscus pump configured to move the resist from the reservoir to the fluid dispenser through a first channel;

[0099] a fluid pump configured to move un-dispensed resist from the fluid dispenser to the reservoir through a second channel;

[0100] a fluid control device communicatively coupled with the fluid pump and the meniscus pump, the fluid control device configured to control operation of the fluid pump and the meniscus pump to maintain a continuous flow of the resist between the reservoir and the fluid dispenser; and

[0101] a stamping mechanism that creates the optical device by applying a stamping template to the resist that has been dispensed onto the substrate, wherein applying the stamping template creates a pattern of one or more structures in the resist, wherein the pattern corresponds to the stamping template.

[0102] Example 2 is the system of Example 1, further comprising:

[0103] a control module communicatively coupled with the fluid control device, the fluid dispenser, and the stamping mechanism, the control module programmed to send signals that control operation of the fluid control device, the fluid dispenser, and the stamping mechanism.

[0104] Example 3 is the system of Example 1 or 2, wherein the fluid dispenser is configured to dispense droplets of the resist that are less than 6 picoliters in volume.

[0105] Example 4 is the system of Example 3, wherein the fluid dispenser is configured to dispense a droplet of the resist having a volume less than 4 picoliters.

[0106] Example 5 is the system of Example 4, wherein the fluid dispenser is configured to dispense a droplet of the resist having a volume less than 2 picoliters.

[0107] Example 6 is the system of any of Examples 1-5, wherein the resist has a refractive index greater than 1.6 for light having a wavelength of 532 nanometers.

[0108] Example 7 is the system of any of Examples 1-6, wherein the substrate has a refractive index in a range of 1.5 to 2.7.

[0109] Example 8 is the system of any of Examples 1-7, wherein the imprint template includes at least two regions of structures having different heights.

[0110] Example 9 is a method for fabricating an optical device, the method comprising:

[0111] operating a fluid dispenser of a dispensing mechanism to dispense a droplet of resist onto a substrate;

[0112] operating a meniscus pump to move the resist through a first channel from a reservoir to the fluid dispenser;

[0113] operating a fluid pump to move un-dispensed resist through a second channel from the fluid dispenser to the reservoir, wherein the fluid pump and the meniscus pump operate to maintain a continuous flow of the resist between the reservoir and the fluid dispenser; and

[0114] operating an imprint mechanism to create the optical device by applying an imprint template to the resist that has been dispensed onto the substrate, wherein applying the imprint template creates a pattern of one or more structures in the resist, wherein the pattern corresponds to the imprint template.

[0115] Example 10 is the method of Example 9, further comprising:

[0116] etching at least a portion of the optical device to reduce a residual layer thickness (RLT) of the resist on the substrate, wherein the etching includes one or more of applying heat or atmospheric etching.

[0117] Example 11 is the method of Example 10, wherein the etching further reduces a size of at least one structure of the pattern created by applying the imprint template.

[0118] Example 12 is a waveguide comprising:

[0119] a substrate; and

[0120] a plurality of structures imprinted into a volume of resist dispensed onto the substrate, wherein the resist is composed of a polymer, wherein a refractive index of the resist is in a range of 1.5 to 2.1, and wherein a residual layer thickness (RLT) of the resist in at least a portion of the substrate is in a range of 0 nm to 50 nm.

[0121] Example 13 is the waveguide of Example 12, wherein the RLT of the resist in at least a portion of the substrate is in a range of 10 to 20 nm.

[0122] Example 14 is the waveguide of Example 12, wherein the RLT of the resist in at least a portion of the substrate is in a range of 20 to 30 nm.

[0123] Example 15 is the waveguide of Example 12, wherein the RLT of the resist in at least a portion of the substrate is in a range of 30 to 40 nm.

[0124] Example 16 is the waveguide of Example 12, wherein the RLT of the resist in at least a portion of the substrate is in a range of 40 to 50 nm.

[0125] Example 17 is the waveguide of any one of Examples 12 to 16, wherein the plurality of structures provide one or more optically active regions comprising one or more of: an input coupler, a combined pupil expander, an exit pupil expander, an orthogonal pupil expander, a recycler, or an anti-reflective feature.

[0126] Example 18 is the waveguide of any one of Examples 12 to 17, wherein the plurality of structures are imprinted with nano-geometries comprising one or more of: binary geometries, tilted geometries, blazed geometries, sawtooth geometries, multi-step geometries, meta-feature geometries, one-dimensional geometries, two-dimensional geometries, or three-dimensional geometries.

[0127] Example 19 is the waveguide of any one of Examples 12 to 18, wherein a refractive index of the substrate is in a range of 1.5 to 2.7.

[0128] Example 20 is the waveguide of any one of Examples 12 to 19, wherein the plurality of structures are imprinted onto a single side of the substrate.

[0129] Example 21 is the waveguide of any one of Examples 12-19, wherein the plurality of structures are imprinted onto both sides of the substrate.

[0130] Example 22 is a nanoimprint lithography method comprising:

[0131] dispensing droplets of resist on a substrate; and

[0132] contacting the resist with an imprint template to create a pattern of one or more structures in the resist, wherein the pattern corresponds to the imprint template;

[0133] polymerizing the resist to create an imprint nanostructure; and

[0134] separating the imprint template from the imprint nanostructure,

[0135] wherein:

[0136] a refractive index of the resist is in a range of 1.5 to 2.1,

[0137] a residual layer thickness (RLT) of the resist in at least a portion of the substrate is in a range of 0 nm to 50 nm, and

[0138] the substrate is composed of an inorganic material.

[0139] Example 23 is the nanoimprint lithography method of Example 22, wherein a volume of each droplet of the resist is less than 6 picoliters, less than 5 picoliters, less than 4 picoliters, 3 picoliters, or less than 2 picoliters.

[0140] Example 24 is the nanoimprint lithography method of Example 23, wherein a volume of each droplet of the resist is less than 1 picoliter.

[0141] Example 25 is the nanoimprint lithography method of any one of Examples 22-24, wherein the RLT of the resist in at least a portion of the substrate is in a range of 0 to 10 nm, 10 to 20 nm, 20 to 30 nm, 30 to 40 nm, or 40 to 50 nm.

[0142] Example 26 is the nanoimprint lithography method of any one of Examples 22-24, wherein the RLT of the resist in at least a portion of the substrate is in a range of 0 to 40 nm, 0 to 30 nm, 0 to 20 nm, or 0 to 10 nm.

[0143] Example 27 is the nanoimprint lithography method of any one of Examples 22-24, wherein the RLT of the resist in at least a portion of the substrate is in a range of 10 to 40 nm or 10 to 30 nm.

[0144] Example 28 is the imprint lithography method of any one of Examples 22-24, wherein the RLT of the resist in at least a portion of the substrate is in a range from 20 to 40 nm.

[0145] Example 29 is the imprint lithography method of any one of Examples 22-28, wherein the substrate comprises glass, LiTaO3, LiNbO3, SiC, or a combination thereof.

[0146] Example 30 is the imprint lithography method of any one of Examples 22-29, wherein the resist is free of inorganic nanoparticles.

[0147] Example 31 is the imprint lithography method of Example 30, wherein the resist has a refractive index in a range from 1.5 to 1.8.

[0148] Example 32 is the imprint lithography method of any one of Examples 22-29, wherein the resist comprises inorganic nanoparticles.

[0149] Example 33 is the imprint lithography method of Example 32, wherein the inorganic nanoparticles comprise TiO2, ZrO2, or both.

[0150] Example 34 is the imprint lithography method of either Example 32 or 33, wherein the inorganic nanoparticles have an average diameter in a range from 5 nm to 15 nm.

[0151] Example 35 is the imprint lithography method of any one of Examples 32-34, wherein the inorganic nanoparticles comprise 10 vol% to 60 vol% of the resist.

[0152] Example 36 is the imprint lithography method of any one of Examples 32-35, wherein the resist has a refractive index in a range from 1.5 to 2.1.

[0153] Example 37 is the imprint lithography method of any one of Examples 22-36, wherein the resist has a viscosity in a range from 5 to 25 centipoise (cP) at 25 °C.

[0154] Example 38 is the imprint lithography method of any one of Examples 22-37, wherein the resist has a surface tension in a range from 20 to 60 millinewtons (mN) per meter (m) at 25 °C.

[0155] Example 39 is the imprint lithography method of any one of Examples 22-38, wherein dispensing the droplet of resist comprises pumping the resist from a reservoir to a fluid dispenser through a first channel.

[0156] Example 40 is the imprint lithography method of any one of Examples 22-39, further comprising: maintaining a continuous flow of the resist between the reservoir and the fluid dispenser.

[0157] Example 41 is the imprint lithography method of Example 40, wherein maintaining a continuous flow of the resist between the reservoir and the fluid dispenser comprises: pumping un-dispensed resist from the fluid dispenser to the reservoir through a second channel.

[0158] Example 42 is the imprint lithography method of any one of Examples 22-38, wherein dispensing the droplets does not require pumping the resist.

[0159] Example 43 is the imprint lithography method of Example 42, wherein dispensing the droplets does not require using a meniscus pump, a fluidic pump, or both to pump the resist.

[0160] While this disclosure includes many specifics, these should not be construed as limiting the scope of the subject matter or of what can be claimed, but as merely providing illustrations of some of the embodiments of the subject matter. The features in the disclosure, which are described in the context of separate embodiments, can also be implemented in combination with each other. Conversely, various features which are described in the context of a single embodiment can also be implemented on a number of embodiments or in any suitable sub-combination. Moreover, although features can be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination and the claimed combination can be directed to a sub-combination or a variation of a sub-combination.

[0161] Specific embodiments of the subject matter have been described. Those of ordinary skill in the art will readily devise numerous other embodiments, alterations, and permutations of the same without the exercise of inventive faculty. Although the operations of some of the disclosed embodiments have been described in a particular, arbitrary order, it should be appreciated that certain embodiments can include performing some operations in a different order, omitting some operations, or performing additional operations not described. It should also be appreciated that structural or logical changes can be made to the order of operations, and that other embodiments can include constructing mechanical or electrical components, or formulas stored in a tangible medium, to perform various

[0162] Thus, the previously described embodiments are not limiting or exhaustive of the disclosure. Other changes, substitutions, and alterations are also possible. The disclosure is not limited to the described embodiments, but rather only by the claims.

Claims

1. A system for fabricating an optical device, the system comprising: a reservoir storing a resist, wherein the resist has a viscosity in a range of 5 to 25 centipoise at 25 °C, a surface tension in a range of 20 to 60 millinewtons at 25 °C, an index of refraction greater than 1.6 for light having a wavelength of 532 nanometers, and wherein the resist includes a plurality of inorganic nanoparticles in a range of 10 vol% to 60 vol% of the resist; a fluid dispenser including a dispensing mechanism configured to dispense droplets of the resist onto a substrate; a meniscus pump configured to move the resist through a first channel from the reservoir to the fluid dispenser; a fluid pump configured to move un-dispensed resist through a second channel from the fluid dispenser to the reservoir; a fluid control device communicatively coupled with the fluid pump and the meniscus pump, the fluid control device configured to control operation of the fluid pump and the meniscus pump to maintain a continuous flow of the resist between the reservoir and the fluid dispenser; and an imprint mechanism creating the optical device by applying an imprint template to the resist that has been dispensed onto the substrate, wherein applying the imprint template creates a pattern of one or more structures in the resist, wherein the pattern corresponds to the imprint template.

2. The system of claim 1, further comprising: a control module communicatively coupled with the fluid control device, the fluid dispenser, and the imprint mechanism, the control module programmed to send signals that control operation of the fluid control device, the fluid dispenser, and the imprint mechanism.

3. The system of claim 1, wherein, the fluid dispenser is configured to dispense droplets of the resist having a volume less than 2 picoliters.

4. The system of claim 1, wherein, the fluid dispenser is configured to dispense droplets of the resist having a volume less than 4 picoliters.

5. The system of claim 1, wherein, the fluid dispenser is configured to dispense droplets of the resist having a volume less than 6 picoliters.

6. The system of claim 1, wherein, the resist has an index of refraction greater than 1.6 for light having a wavelength of 532 nanometers.

7. The system of claim 1, wherein, the substrate has an index of refraction in a range of 1.5 to 2.

7.

8. The system of claim 1, wherein, the imprint template includes at least two regions of structures having different heights.

9. A method for fabricating an optical device, the method comprising: operating a fluid dispenser including a dispensing mechanism to dispense droplets of a resist onto a substrate, wherein the resist has a viscosity in a range of 5 to 25 centipoise at 25 °C, a surface tension in a range of 20 to 60 millinewtons at 25 °C, an index of refraction greater than 1.6 for light having a wavelength of 532 nanometers, and wherein the resist includes a plurality of inorganic nanoparticles in a range of 10 vol% to 60 vol% of the resist; operating a meniscus pump to move the resist through a first channel from a reservoir to the fluid dispenser; operating a fluid pump to move un-dispensed resist through the second channel from the fluid dispenser to the reservoir, wherein the fluid pump and the meniscus pump operate to maintain continuous flow of the resist between the reservoir and the fluid dispenser; and operating a stamping mechanism to create the optical device by applying a stamping template to the resist that has been dispensed onto the substrate, wherein applying the stamping template creates a pattern of one or more structures in the resist, wherein the pattern corresponds to the stamping template.

10. The method of claim 9, further comprising: etching at least a portion of the optical device to reduce a residual layer thickness (RLT) of the resist on the substrate, wherein the etching includes one or more of applying heat or atmospheric etching.

11. The method of claim 10, wherein, the etching further reduces a size of at least one structure of the pattern created by applying the stamping template.

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