Micro light emitting diode system with immersion lens

Abstract

A micro light emitting diode (microLED) assembly including a package or substrate including a volume, a microLED arranged in the volume, and a lens optically coupled to the microLED. An immersion material is arranged in contact with the microLED. The lens may seal the immersion material in the volume. Alternatively, a cover window may be used to seal the immersion material in the volume, and the lens connected to the cover window. The package may include one or more ports that allow the volume to be filled with the immersion material and / or allow the immersion material to be circulated through the volume. The microLED assembly may be used in conjunction with a projection lens and / or an X-cube prism to emit image-bearing light into an image light guide for formation of a virtual image.

Description

MICRO LIGHT EMITTING DIODE SYSTEM WITH IMMERSION LENSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under Articles 4 and 8 of the Stockholm Act of the Paris Convention for the protection of Industrial Property of U.S. Patent Application No. 63 / 574,308, filed on April 4, 2024, which application is incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure generally relates to electronic displays, and more particularly, to a micro light emitting diode (microLED) system with a liquid immersion lens for enhanced light extraction.BACKGROUND

[0003] Head-Mounted Displays (HMDs) can include an image source and, in some examples, an image light guide for presenting virtual images to a wearer’s eyes. The image light guide can be arranged for conveying the virtual images from an offset position of the image source to a position aligned with the wearer’s eye. For many applications, there is particular value in forming a virtual image that can be visually superimposed over the real-world image that lies in the field of view of the HMD user.

[0004] The image source may utilize a microLED, also known as a pLED or micro LED. However, most light generated in a microLED is trapped by total internal reflection (TIR) inside the microLED because of a large difference in refractive index between the microLED and surrounding environment, e.g., air. Such trapped light can also lead to pixel-to-pixel crosstalk.SUMMARY

[0005] The present disclosure is directed to one or more exemplary embodiments of a microLED assembly including a package or substrate comprising a volume, a microLED arranged in the volume, and a lens optically coupled to the microLED. An immersion material is arranged in contact with and surrounding at least a portion of the microLED. The lens may seal the immersion material in the volume. Alternatively, a cover window may be used to seal the immersion material in the volume. The cover window can be used in in addition to the lens where the lens is connected to the cover window. In some examples, the package may include one or more ports that allow the volume to be filled with the immersion material and / or allow the immersion material to be circulated through the volume. The microLED assembly may be used in conjunction with a projection lens and / or an X-cube prism or other RGB combiner / splitter prism to emit imagebearing light into an image light guide or waveguide for formation of a virtual image.

[0006] The present disclosure is directed to one or more exemplary embodiments of a microLED assembly.

[0007] In an exemplary embodiment, the microLED assembly comprises a package including a volume, a microLED arranged in the volume, and a lens optically coupled to the microLED, wherein an immersion material is arranged between the microLED and the lens. In an exemplary embodiment, the package further comprises a bottom surface and a lateral surface, the volume is bounded, at least in part, by the bottom surface and the lateral surface, and the microLED is secured to the bottom surface. In an exemplary embodiment the microLED comprises a transistor backplane secured to a bottom surface of the package, and a light emitting frontplane connected to the transistor backplane.

[0008] In an exemplary embodiment, the package further comprises a first rear surface and a first front surface, and the microLED is spaced apart from the first front surface. In an exemplary embodiment, the lens comprises a planar surface connected to the package, and at least one curvilinear surface extending from the planar surface in a first direction. In an exemplary embodiment, the planar surface is directly connected to the first front surface of the package and encloses the volume. In an exemplary embodiment, the microLED assembly further comprises a cover window or cover glass, including a second rear surface connected to the first front surface, and a second front surface. In an exemplary embodiment, the second rear surface is directly connected to the first front surface and encloses the volume, and the planar surface is directly connected to the second front surface.

[0009] In an exemplary embodiment, the lens is a half ball lens. In an exemplary embodiment, the lens is a truncated half ball lens. In an exemplary embodiment, the lens is a diffractive lens or metalens. In an exemplary embodiment, the lens is a plano-convex lens. In an exemplary embodiment, the package further comprises at least one port extending to the volume from an outer surface of the package. In an exemplary embodiment, the package comprises a first port and a second port extending from the first rear surface to the volume in a first direction. In an exemplary embodiment, the immersion material is sealed in the volume by the lens or a cover window. In an exemplary embodiment, the immersion material comprises a silicone fluid. In an exemplary embodiment, the immersion material comprises an oil. In an exemplary embodiment, the immersion material comprises an optical fluid. In an exemplary embodiment, the immersion material comprises glycerol.

[0010] In an exemplary embodiment, the immersion material (60) comprises a refractive index greater than or equal to 1.4 and less than or equal to 1.8. In an exemplary embodiment, the immersion material (60) comprises an electrical resistivity of greater than 108ohm-cm. In anexemplary embodiment, the immersion material (60) comprises a freezing point of less than - 10°C. In an exemplary embodiment, the lens (80) comprises a first refractive index, the immersion material (60) comprises a second refractive index, and the absolute value of the difference between the first refractive index and the second refractive index is greater than 0.1. In an exemplary embodiment, light emitted by the microLED assembly (10) travels from, in order, the microLED (40), through the immersion material (60), and then through the lens (80).

[0011] The present disclosure is directed to one or more exemplary embodiments of a microLED display system.

[0012] In an exemplary embodiment, the microLED display system comprises an image source arranged to emit image-bearing light, including a projection lens, and at least one microLED assembly, the microLED assembly comprising a package including a volume, a microLED arranged in the volume, and a lens optically coupled to the microLED, wherein an immersion material is arranged between the microLED and the lens, and an image light guide including an in-coupling diffractive optic operable to couple the image-bearing light into the image light guide, and an out-coupling diffractive optic operable to form a virtual image that is viewable from a viewer eyebox.

[0013] In an exemplary embodiment, the microLED display system further comprises an X-cube prism optically arranged between the at least one microLED assembly and the projection lens.

[0014] These and other aspects, objects, features, and advantages of the present disclosure will be more clearly understood and appreciated from the following detailed description of the embodiments and appended claims, and by reference to the accompanying drawing figures.BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0015] The accompanying drawings are incorporated herein as part of the specification. The drawings described herein illustrate embodiments of the presently disclosed subject matter and are illustrative of selected principles and teachings of the present disclosure. However, the drawings do not illustrate all possible implementations of the presently disclosed subject matter and are not intended to limit the scope of the present disclosure in any way.

[0016] FIG. l is a cross-sectional view of a microLED assembly.

[0017] FIG. 2 is a cross-sectional view of a microLED assembly.

[0018] FIG. 3 is a cross-sectional view of a microLED assembly.

[0019] FIG. 4 is a cross-sectional view of a microLED assembly showing light ray paths therefrom.

[0020] FIG. 5 is a detail view of the microLED assembly taken generally along DETAIL 5 in FIG.4.

[0021] FIG. 6 is a cross-sectional view of a microLED assembly showing light ray paths therefrom.

[0022] FIG. 7 is a detail view of the microLED assembly taken generally along DETAIL 7 in FIG. 6.

[0023] FIG. 8 shows a graph comparing outcoupled light intensity of the microLED assembly shown in FIG. 1 and a non-immersion lens microLED assembly, for red light.

[0024] FIG. 9 shows a graph comparing outcoupled light intensity of the microLED assembly shown in FIG. 1 and a non-immersion lens microLED assembly, for green light.

[0025] FIG. 10 shows a graph comparing outcoupled light intensity of the microLED assembly shown in FIG. 3 and a non-immersion lens microLED assembly, for red light.

[0026] FIG. 11 shows a graph illustrating the percentage of outcoupled light as a function of refractive index at the interface with a microLED.

[0027] FIG. 12 is a top view of a microLED display system including an image light guide with an exaggerated thickness for showing the propagation of light from an image source along the image light guide to an eyebox within which the virtual image can be viewed.

[0028] FIG. 13 is a perspective view of an image light guide including an in-coupling diffractive optic, a turning diffractive optic, and an out-coupling diffractive optic for managing the propagation of image-bearing light beams.

[0029] FIG. 14 is a top view of a microLED display system including an image light guide with an exaggerated thickness for showing the propagation of light from an image source along the image light guide to an eyebox within which the virtual image can be viewed.

[0030] FIG. 15 is a top view of a microLED display system including an image light guide with an exaggerated thickness for showing the propagation of light from an image source along the image light guide to an eyebox within which the virtual image can be viewed.DETAILED DESCRIPTION

[0031] It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application.

[0032] Where used herein, the terms “first,” “second,” and so on, do not necessarily denote any ordinal, sequential, or priority relation, but are simply used to more clearly distinguish one element or set of elements from another, unless specified otherwise.

[0033] Where used herein, the terms “viewer,” “operator,” “observer,” “wearer,” and “user” are considered equivalents and refer to the person or machine who wears and / or views images using a head mounted device.

[0034] Where used herein, the term “set” refers to a non-empty set, as the concept of a collection of elements or members of a set is widely understood in elementary mathematics. The term “subset,” unless otherwise explicitly stated, is used herein to refer to a non-empty proper subset, that is, to a subset of the larger set, having one or more members. For a set S, a subset may comprise the complete set S. A “proper subset” of set S, however, is strictly contained in set S and excludes at least one member of set S.

[0035] Where used herein, the terms “coupled,” “coupler,” or “coupling” in the context of optics refer to a connection by which light travels from one optical medium or device to another optical medium or device.

[0036] Where used herein, the term “beam expansion” is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions. Similarly, where used herein, the terms “expanded image-bearing light beams” and “expanded set of angularly related beams” refer to a light beam replicated via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions.

[0037] Where used herein, the term “about” when applied to a value is intended to mean within the tolerance range of the equipment used to produce the value, or, in some examples, is intended to mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified.

[0038] Where used herein, the term “substantially” is intended to mean within the tolerance range of the equipment used to produce the value, or, in some examples, is intended to mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified.

[0039] Where used herein, the term “exemplary” is intended to mean “an example of,” “serving as an example,” or “illustrative,” and does not denote any preference or requirement with respect to a disclosed aspect or embodiment.

[0040] One skilled in the relevant art will recognize that the elements and techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects of the present disclosure.Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” throughout the specification is not necessarily referring to the same embodiment. However, the particular features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0041] Adverting now to the figures, FIG. 1 is a cross-sectional view of microLED assembly 10. MicroLED assembly 10 generally comprises package 20, microLED 40, immersion material 60, and lens 80. In an exemplary embodiment, microLED assembly 10 further comprises cover window 70.

[0042] Package 20 comprises rear surface 22, front surface 24, and perimeter surface 26. Perimeter surface 26 extends from rear surface 22 to front surface 24 in direction DI. In an exemplary embodiment, front surface 24 is arranged parallel to rear surface 22. In an exemplary embodiment, front surface 24 is arranged nonparallel to rear surface 22. In an exemplary embodiment, package 20 further comprises a recess or volume 28 that extends into package 20 from front surface 24 in direction D2. Package 20 further comprises a bottom surface 30 and a lateral surface 32 where volume 28 is bounded, at least in part, by bottom surface 30 and lateral surface 32 of package 20. Bottom surface 30 is spaced apart from rear surface 22 in direction DI. In an exemplary embodiment, bottom surface 30 is arranged parallel to front surface 24. In an exemplary embodiment, volume 28 is arranged between and spaced apart from perimeter surface 26. Volume 28 is operatively arranged to hold immersion material 60 to immerse microLED 40, as will be described in greater detail below.

[0043] In an exemplary embodiment, package 20 may further comprise one or more ports, for example, port 34 and port 36, operatively arranged to fill volume 28 with immersion material 60 from rear surface 22. In other exemplary embodiments, ports, e.g., port 36 and / or port 36 may be arranged on, in, or through perimeter surface 26 and / or front surface 24. Using port(s) 34, 36 to fill volume 28 with immersion material 60 may be advantageous when lens 80 and / or cover window 70 are secured over volume 28 on front surface 24 prior to injection of immersion material 60. In some exemplary embodiments, one of port 34 and port 36 may operate as the inlet and the other of port 34 and port 36 may operate as the air or gas release or outlet. Once volume 28 is filled with immersion material 60 ports 34 and 36 are sealed using any suitable means, for example, plugs, sealant, or the like.

[0044] In an exemplary embodiment, ports 34 and 36 may be utilized to circulate immersion material 60 through microLED assembly 10 in order to regulate the temperature of the componentsthereof (i.e., heating or cooling). For example, one of port 34 and port 36 may operate as the inlet and the other of port 34 and port 36 may operate as the outlet. Continuing the example, immersion material 60 may flow into volume 28 through port 34, pass over microLED 40, and exit volume 28 through port 36. In an exemplary embodiment, immersion material 60 may continuously flow through microLED assembly 10 or circulate when necessary, for example, in response to the temperature of microLED assembly 10 falling outside of a predetermined range, for example, 0- 100°C (i.e., a signal from a temperature sensor or thermostat). In an exemplary embodiment, package 20 comprises ceramic. In an exemplary embodiment, package 20 comprises metal.

[0045] MicroLED 40 comprises transistor backplane 42 and light emitting frontplane 50. Transistor backplane 42 is arranged within volume 28 and proximate to or engaged with bottom surface 30 of package 20. Transistor backplane 42 may comprise circuitry / electronics. In an exemplary embodiment, a silicon substrate or base is arranged between transistor backplane 42 and bottom surface 30. In an exemplary embodiment, transistor backplane 42 may comprise complementary metal-oxide semiconductor (CMOS) transistors.

[0046] Light emitting frontplane 50 is arranged on transistor backplane 42 and may comprise one or more microLED arrays. In an exemplary embodiment, light emitting frontplane 50 may comprise the LED epitaxy. In an exemplary embodiment, light emitting frontplane 50 may be connected to transistor backplane 42 via a metal bonding layer arranged therebetween. In an exemplary embodiment, the frontplane 50 comprises a light emitting material, e.g., gallium nitride (GaN) or aluminum gallium indium phosphide (AlGalnP), and a transparent substrate material, e.g., sapphire. In this exemplary embodiment, interface 52 is formed between the sapphire substrate and the surrounding immersion material 60 in volume 28. In some exemplary embodiments, frontplane 50 comprises a light emitting material, e.g., GaN or AlGalnP, and does not comprise a transparent substrate material. In these exemplary embodiments interface 52 is formed between the light emitting material and the surrounding immersion material 60 within volume 28. MicroLED 40 is arranged below and spaced apart from front surface 24. As such, immersion material 60 is arranged between microLED 40 and cover window 70 and / or lens 80. In some examples, volume 28 is bounded by bottom surface 30, lateral surface 32, and cover window 70 or lens 80.

[0047] Immersion material 60 preferably comprises a high refractive index material. A higher refractive index results in higher extraction efficiency (i.e., less loss of light due to total internal reflection). It is desired that immersion material 60 be optically clear, have a relatively high refractive index, for example 1.4-2.0 or preferably 1.4-1.8, have a high electrical resistivity (e.g., a volume resistivity greater than 108ohm-cm), is stable under exposure to light and / or change intemperature, is chemically stable, has a relatively low viscosity (e.g., less than 10,000 cP), and has a low toxicity. Some standard liquid materials with a high refractive index that are used as refractive index fluids are unstable upon extended exposure to light, toxic, and corrosive and thus are not desirable for use in microLED assembly 10. Some advantages of immersing microLED 40 in immersion material 60 include 1) no structural stress, 2) enhanced heat exchange and transport, 3) low thermal expansion, and 4) mechanical and optical stability.

[0048] In an exemplary embodiment, lens 80 has a significantly higher refractive index than immersion material 60. For example, the absolute value of the difference in refractive index between the material of lens 80 and immersion material 60 is greater than 0.1.

[0049] In an exemplary embodiment, immersion material 60 is rated for a broad operating temperature for use in certain environments (e.g., an outdoor environment). For example, for cold outdoor environments, immersion material 60 must still flow at a very low temperature. In an exemplary embodiment, immersion material 60 comprises a freezing point of less than -10°C, or preferably less than -20°C.

[0050] In an exemplary embodiment, immersion material 60 comprises a silicone fluid. For example, immersion material 60 may comprise a silicone fluid with a high refractive index such as GELEST® phenylmethylsiloxane oligomer silicone fluid, product code PDM-7040, with a refractive index of n=1.556 and a viscosity of 40 cSt at 25°C. In an exemplary embodiment, immersion material 60 may comprise a silicone fluid with a high refractive index such as GELEST® phenylmethylsiloxane oligomer silicone fluid, product code PDM-7050, with a refractive index of n=1.588 and a viscosity of 170 cSt at 25°C.

[0051] In an exemplary embodiment, immersion material 60 comprises a polymer fluid. For example, immersion material 60 may comprise DOW DOWSIL® polyphenylmethyldimethylsiloxane polymer fluid, with a refractive index of 1.5, a volume resistivity of 1014ohm-cm, a viscosity of 100 cSt at 25°C, and a freezing point of -50°C. In an exemplary embodiment, immersion material 60 may comprise DOW DOWSIL® polyphenylmethyldimethylsiloxane fluid, with a refractive index of 1.533, a volume resistivity of 1013ohm-cm, a viscosity of 500 cSt at 25°C, and a freezing point of -22°C.

[0052] In an exemplary embodiment, immersion material 60 comprises an optical fluid or a SANTOLUBES® fluid. For example, immersion material 60 may comprise SANTOVAC® MCS-293 high performance fluid with a refractive index of n=l .671, a viscosity of 25 cSt at 40°C, and a pour point of -29°C. In an exemplary embodiment, immersion material 60 may comprise SANTOLIGHT™ SL-5267 optical fluid with a refractive index of n=1.67, a volume resistivity of 1015ohm-cm, a viscosity of 100 cP at 25°C, and a glass transition point of -40°C. In an exemplaryembodiment, immersion material 60 may comprise SANTOLIGHT™ SL-5262 optical fluid with a refractive index of n=1.62, a volume resistivity of 1015ohm-cm, a viscosity of 650 cP at 25°C, and a glass transition point of -30°C.

[0053] In an exemplary embodiment, immersion material 60 may comprise an oil such as microscope refractive index oil with a refractive index of n=1.51. In an exemplary embodiment, immersion material 60 may comprise CARGILLE® laboratories immersion oil type A, with a refractive index of 1.515, a viscosity of 138 cP at 23°C, and a freezing point of -13°C. In an exemplary embodiment, immersion material 60 may comprise CARGILLE® laboratories immersion oil type B, with a refractive index of 1.515, a viscosity of 1153 cP at 23°C, and a freezing point of -13 °C.

[0054] In an exemplary embodiment, immersion material 60 comprises glycerol. For example, immersion material 60 may comprise 100% glycerol with a refractive index of n=l .47, a viscosity of 1500 cP at 20°C, and a freezing point of 17°C. In an exemplary embodiment, immersion material 60 comprises a mixture of glycerol and water.

[0055] In an exemplary embodiment, immersion material 60 may comprise a fluid with a low refractive index. For example, immersion material 60 may comprise 3M® FLUORINERT® electronic liquid FC-70 with a refractive index of 1.3, a volume resistivity of 2.3 x 1015ohm-cm, a viscosity of 24 cP at 25°C, and a pour point of -25°C. In such exemplary embodiments, the use of a relatively low refractive index fluid (e.g., 1.3) with a relatively high index lens 80 and / or cover window 70 may provide a good angular concentration of light in a forward direction, namely, direction DI.

[0056] In an exemplary embodiment, immersion material 60 comprises an immersion material with high index nanoparticles (e.g., TiO2). In an exemplary embodiment, immersion material 60 is a fluid immersion material. In an exemplary embodiment, immersion material 60 is a liquid immersion material.

[0057] Immersion material 60 is sealed in volume 28 by cover window 70 and / or lens 80. As shown in FIG. 1, cover window 70 seals immersion material 60 in volume 28. Cover window 70 comprises rear surface 72, front surface 74, and perimeter surface 76. Rear surface 72 is connected to front surface 24 of package 20 to seal or contain immersion material 60 in volume 28. Rear surface 72 may be bonded or connected to front surface 24 of package 20 using any suitable means, e.g., adhesive or mechanical fixtures such as clamps, screws, pins, etc. Cover window 70 is larger than the width or diameter of volume 28 so as to completely enclose immersion material 60 in volume 28. Cover window 70 may comprise sapphire, SHOTT N-BK7® optical glass, floatglass, CORNING GORILLA® glass, fused silica, or any other transparent material. In some exemplary embodiments cover window 70 comprises a high refractive index material.

[0058] As shown in FIG. 1, lens 80 is connected to cover window 70. In an exemplary embodiment, lens 80 comprises planar surface 82 connected to front surface 74 of cover window 70, and a curvilinear surface 84. Planar surface 82 may be connected or bonded to cover window 70 using any suitable means, e.g., optical adhesive. As shown, lens 80 is a half ball or hemispherical lens having height Hl (i.e., radius) and width W1 (i.e., diameter), wherein width W1 is equal to double height HL Width W1 is greater than the width of microLED 40, which allows lens 80 to refract light toward a desired direction, for example, direction DI. Lens 80 has a high aspect ratio and is optically coupled to microLED 40 to enhance extraction of light that would otherwise be trapped via TIR and lost. Lens 80 may comprise sapphire, SHOTT N-BK7® optical glass, float glass, CORNING GORILLA® glass, fused silica, a glass with high refractive index, or any other transparent optical material. Additionally, when compared to air, the arrangement of immersion material 60 in volume 28 may bend light more toward the normal since, immersion material 60 has a higher refractive index than air. It should be appreciated that lens 80 may comprise a thin shell filled with a liquid. It should be appreciated that lens 80 can also be a truncated half-ball lens or truncated hemispherical lens. In an exemplary embodiment, lens 80 is rigidly secured to package 20. Light emitted by microLED assembly 10 travels, in order, from microLED 40 (i.e., through frontplane 50), through immersion material 60, through cover window 70, and through lens 80.

[0059] FIG. 2 is a cross-sectional view of microLED assembly 10. In this exemplary embodiment, microLED assembly 10 does not include cover window 70. Instead, microLED assembly 10 comprises lens 80 which seals immersion material 60 in volume 28. In an exemplary embodiment, lens 80 comprises a planar surface 82 and a curvilinear surface 84. Planar surface 82 is connected to front surface 24 of package 20 to seal and contain immersion material 60 in volume 28. Planar surface 82 may be connected or secured to front surface 24 using any suitable means, e.g., optical adhesive. Planar surface 82 is larger than the diameter or width of volume 28 so as to completely enclose immersion material 60 in volume 28. As shown in FIG. 2, lens 80 is a truncated half ball or sphere lens having height H2 and width W2, wherein width W2 is greater than double height H2. Width W2 is greater than the width of microLED 40, which allows lens 80 to refract light toward a desired direction, for example, direction DI. Lens 80 has a high aspect ratio and is optically coupled to microLED 40 to enhance extraction of light that would otherwise be trapped via TIR and lost. Lens 80 may comprise sapphire, SHOTT N-BK7® optical glass, CORNING GORILLA® glass, fused silica, a glass with high refractive index, or any other transparent opticalmaterial. It should be appreciated that lens 80 may comprise a thin shell filled with a liquid. Light emitted by microLED assembly 10 travels, in order, from microLED 40 (i.e., from frontplane 50), through immersion material (60), and through lens 80.

[0060] FIG. 3 is a cross-sectional view of microLED assembly 10. As described above, microLED assembly 10 generally comprises package or substrate 20, microLED 40, immersion material 60, and lens 80. In an exemplary embodiment, microLED assembly 10 further comprises cover window 70. As shown in FIG. 3, microLED assembly 10 includes lens 80. Lens 80 is connected to cover window 70. In an exemplary embodiment, lens 80 comprises planar surface 82, spherical or curvilinear surface 84, and cylindrical surface 86. Planar surface 82 may be connected or secured to cover window 70 using any suitable means (e.g., optical adhesive). As shown, cylindrical surface 86 extends from planar surface 82 in direction DI. In an exemplary embodiment, cylindrical surface 86 is perpendicular to planar surface 82. Curvilinear surface 84 is a convex surface resembling a truncated half ball or sphere shape. Cylindrical surface 86 has height H4 and lens 80 has a total height of H3, which is greater than H4. Lens 80 has width W3 which is greater than both height H3 and height H4. Width W3 is greater than the width of microLED 40, which allows lens 80 to diffract or refract light toward a desired direction, for example, direction DI. Lens 80 may comprise sapphire, SHOTT N-BK7® optical glass, float glass, CORNING GORILLA® glass, fused silica, a glass with high refractive index, or any other transparent optical material. It should be appreciated that lens 80 may comprise a thin shell filled with a liquid. In an exemplary embodiment, lens 80 may comprise a diffractive lens, metamaterial, metasurface, and / or metalens. It should be appreciated that, in examples where meta materials are used, the material properties of the metamaterials can be selected from any material having subwavelength structures that are configured to emulate the optical properties of a lens, e.g., a concave, convex, or other optical element, without requiring that the surface of the optical structure be curved. In other words, although the lens 80 disclosed in the present disclosure may include planar or curved surfaces, a metamaterial disposed on one or more surfaces of these features may cause light rays and / or electromagnetic wavefronts associated with light passing through these features to behave as though they were passing through a shaped lens or a lens of a different shape than physically presented.

[0061] FIG. 4 is a cross-sectional view of microLED assembly 10, showing light ray paths therefrom. FIG. 5 is a detail view of MicroLED assembly 10 taken generally along DETAIL 5 in FIG. 4. As shown, light rays 2A-2I are projected by microLED 40 generally in direction DI. Specifically, light rays 2A-2I are emitted in frontplane 50 (i.e., from a light-emitting layer in frontplane 50). Light rays 2A-2B and 2H-2I become trapped in frontplane 50 due to TIR, whereaslight rays 2C-2G travel through frontplane 50, immersion material 60, cover window 70, and lens 80. The arrangement of immersion material 60 between microLED 40 and cover window 70 and / or lens 80 decreases the light trapped in frontplane 50 (i.e., reduces TIR) and thus increases the amount of light outcoupled from microLED 40.

[0062] In the exemplary embodiment shown, light rays 2A-2I are emitted in frontplane 50 at - 63.4°, -45°, -26.6°, -14°, 0°, 14°, 26.6°, 45°, and 63.4°, respectively, relative to direction DI. In an exemplary embodiment, microLED 40 has a refractive index of 2.47, immersion material has a refractive index of 1.5, cover window 70 has a refractive index of 1.5, and lens 80 has a refractive index of 1.5. Since immersion material 60, cover window 70, and lens 80 have the same refractive index, there is very little or no refraction of light rays 2C-2G as they travel therebetween. It should be appreciated that if, instead of immersion material 60, air was arranged between microLED 40 and cover window 70 and / or lens 80, light ray 2C and light ray 2G would also become trapped inside frontplane 50. Thus, the use of immersion material 60 provides a significant improvement in light output. It should be appreciated that more light rays than those illustrated are emitted in frontplane 50. The rays shown are selected to illustrate only a limited number of exemplary rays and the effects between their angular relationship, TIR, and the various surfaces / interfaces they encounter prior to exiting microLED assembly 10.

[0063] FIG. 6 is a cross-sectional view of microLED assembly 10, showing light ray paths therefrom. FIG. 7 is a detail view of MicroLED assembly 10 taken generally along DETAIL 7 in FIG. 6. As shown, light rays 2A-2I are projected by microLED 40 generally in direction DI. Specifically, light rays 2A-2I are emitted in frontplane 50. Light rays 2A-2B and 2H-2I become trapped in frontplane 50 due to TIR, whereas light rays 2C-2G travel through frontplane 50, immersion material 60, cover window 70, and lens 80. The arrangement of immersion material 60 between microLED 40 and cover window 70 and / or lens 80 decreases the light trapped in frontplane 50 (i.e., reduces TIR) and thus increases the amount of light outcoupled from microLED 40.

[0064] In the embodiment shown, light rays 2A-2I are emitted in frontplane 50 at -63.4°, -45°, - 26.6°, -14°, 0°, 14°, 26.6°, 45°, and 63.4°, respectively, relative to direction DI. In an exemplary embodiment, microLED 40 has a refractive index of 2.47, immersion material has a refractive index of 1.5, cover window 70 has a refractive index of 1.5, and lens 80 has a refractive index of 1.9. Since immersion material 60 and cover window 70 have the same diffractive index, there is very little or no refraction of light rays 2C-2G as they travel therebetween. Due to the differences in refractive index between other materials, light rays bend as they travel therebetween. For example, light ray 2G is emitted in frontplane 50 at angle a (e.g., 26.6°) relative to direction DI.Upon entering immersion material 60, light ray 2G is refracted altering its path to angle P (i.e., the angle of refraction) relative to direction DI. In an exemplary embodiment, angle P is greater than angle a. Light ray 2G is not refracted upon entering cover window 70, since the refractive index of immersion material 60 and cover window 70 are the same. Upon entering lens 80, light ray 2G is refracted altering its path to angle y relative to direction DI . In an exemplary embodiment, angle y is less than angle p. Upon leaving lens 80, light ray 2G may be further refracted altering its path to angle 5 relative to direction DI. In an exemplary embodiment, angle 5 is less than angle y.

[0065] As shown, the arrangement of lens 80 (an / or cover window 70) may help to direct light closer to the normal. Specifically, light rays may exit microLED 40 at a rather wide angle (e.g., 50°) relative to direction DI, but cover window 70 and / or lens 80 will typically bend the light rays back toward the normal, namely, direction DI (e.g., 85°), and into a narrower and more directed cone angle making microLED 40 more angularly concentrated for efficient collection by a subsequent optical system. This occurs when cover window 70 comprises a higher refractive index material than immersion material 60 and / or lens 80 comprises a higher refractive index material than cover window 70. It should be appreciated that if, instead of immersion material 60, air was arranged between microLED 40 and cover window 70 and / or lens 80, light ray 2C and light ray 2G would also become trapped inside frontplane 50. Thus, the use of immersion material 60 provides a significant improvement in light output.

[0066] FIG. 8 shows graph 200 comparing outcoupled light intensity of microLED assembly 10 with a half ball lens as shown in FIG. 1 and a non-immersion lens assembly (i.e., without immersion material) for red light. Line 204 shows outcoupled light intensity of microLED assembly 10, wherein microLED 40 is immersed in immersion material 60 and half ball lens 80 is used. In this exemplary embodiment, immersion material 60 comprises DOW DOWSIL® 550 silicone fluid with a refractive index of n~1.50, window 70 comprises microscope cover glass with a refractive index of n~1.51, lens 80 comprises a EDMUNDS OPTICS® 8mm diameter, half ball lens made from SHOTT N-BK7® optical glass with a refractive index of n~1.51, wherein lens 80 is bonded to window 70, for example, using NORLAND® optical adhesive NOA 63 with a refractive index of n~1.56. Line 202 shows outcoupled light intensity of microLED assembly 10 wherein microLED 40 is immersed in air. The results show significant increase in outcoupled light, with 1.92x gain on axis and 1.82x gain at ±30°.

[0067] FIG. 9 shows graph 210 comparing outcoupled light intensity of microLED assembly 10 shown in FIG. 1 and a non-immersion lens microLED assembly, for green light. Line 214 shows outcoupled light intensity of microLED assembly 10, wherein microLED 40 is immersed in immersion material 60 and half ball lens 80 is used. In this exemplary embodiment, immersionmaterial 60 comprises DOW DOWSIL® silicone fluid with a refractive index of n~1.50, window 70 comprises microscope cover glass with a refractive index of n~1.51, lens 80 comprises a EDMUNDS OPTICS® 8mm diameter, SHOTT N-BK7® optical glass half ball lens with a refractive index of n~1.51, wherein lens 80 is bonded to window 70, for example, using NORLAND® optical adhesive NOA 63 with a refractive index of n~1.56. Line 212 shows outcoupled light intensity of microLED assembly 10 wherein microLED 40 is immersed in air. The results show an increase in outcoupled light, with 1.29x gain on axis and 1.32x gain at ±30°.

[0068] FIG. 10 shows graph 220 comparing outcoupled light intensity of microLED assembly 10 shown in FIG. 3 and a non-immersion lens microLED assembly, for red light. Line 224 shows outcoupled light intensity of microLED assembly 10, wherein microLED 40 is immersed in fluid 60 and plano-convex lens 80 is used. In this exemplary embodiment, immersion material 60 comprises DOW DOWSIL® 550 silicone fluid with a refractive index of n~1.50, window 70 comprises microscope cover glass with a refractive index of n~1.51, lens 80 comprises a EDMUNDS OPTICS® 6mm diameter, 6mm focal length, N-SF11 plano-convex lens with a refractive index of n~1.78. Line 222 shows outcoupled light intensity of microLED assembly 10 wherein microLED 40 is immersed in air. The results show significant increase in outcoupled light, with 1.47x gain on axis and 1.70x gain at ±30°.

[0069] Thus, the immersion of microLED 40 in immersion material 60, as well as optically coupling lens 80 to microLED 40, can significantly increase light outcoupling from microLED 40 increasing light extraction of the microLED assembly 10. The results showing an increase in outcoupled light is expected with both LED assemblies and microLED assemblies.

[0070] FIG. 11 shows graph 230 illustrating the percentage of outcoupled light of microLED assembly 10 as a function of the refractive index at the interface. A refractive index of 1 corresponds to air (i.e., no immersion material) and a refractive index generally in the range of 1.4-1.8 corresponds to immersion material 60. Line 232 shows the percent of microLED emitted light in sapphire that is outcoupled at a flat interface with a lower index material. Line 234 shows the percent of microLED emitted light in GaN that is outcoupled at a flat interface with a lower index material. It is apparent for both cases, lines 232 and 234, that increasing the refractive index of immersion material 60 increases the percentage of outcoupled light.

[0071] FIG. 12 is a top view of microLED display system 300 including image light guide 310 with an exaggerated thickness T for showing the propagation of light from image source 318 along the image light guide 310 to an eyebox E within which the virtual image can be viewed. Image light guide 310 may comprise image light guide 310 having plane-parallel surfaces 312, 314. Image light guide 310 comprises transparent substrate S, which, for example, can be made ofoptical glass or plastic, having plane parallel first and second surfaces 312, 314. In this example, in-coupling diffractive optic IDO and out-coupling diffractive optic ODO are arranged on second surface 314, and in-coupling diffractive optic IDO is a reflective-type diffraction surface relief grating through which image-bearing light WI is coupled into image light guide 310. However, in-coupling diffractive optic IDO could alternately be a volume hologram or other holographic diffraction element, a liquid crystal material, or other type of optical component that provides diffraction for the incoming, image-bearing light WI. In-coupling diffractive optic IDO can be located on, in, or engaged with first surface 312 or second surface 314 of image light guide 310 and can be of a transmissive or reflective type depending upon the direction from which imagebearing light WI approaches image light guide 310.

[0072] When used as a part of a virtual display system, in-coupling diffractive optic IDO couples image-bearing light WI from real image source 318 into substrate S of image light guide 310. Any real image or image dimension is first converted into an array of overlapping angularly related beams encoding the different positions within an image for presentation to in-coupling diffractive optic IDO. Image-bearing light WI is diffracted (generally through a first diffraction order) and thereby redirected by in-coupling diffractive optic IDO into image light guide 310 as imagebearing light WG for further propagation along image light guide 310 by TIR. Although diffracted into a generally more condensed range of angularly related beams in keeping with the boundaries set by TIR, image-bearing light WG preserves the image information in an encoded form. Out- coupling diffractive optic ODO receives the encoded image-bearing light WG and diffracts (also generally through a first diffraction order) image-bearing light WG out of image light guide 310 as image-bearing light WO toward the intended location of a viewer’s eye. Generally, out- coupling diffractive optic ODO is designed symmetrically with respect to in-coupling diffractive optic IDO to restore the original angular relationships of image-bearing light WI among outputted angularly related beams of image-bearing light WO. However, to increase at least one dimension of overlap among the angularly related beams in a so-called eyebox E within which the virtual image can be seen, out-coupling diffractive optic ODO is arranged to encounter image-bearing light WG multiple times and to diffract only a portion of image-bearing light WG on each encounter. The multiple encounters along one dimension of out-coupling diffractive optic ODO have the effect of enlarging one dimension of each of the angularly related beams of image-bearing light WO thereby expanding one dimension of eyebox E within which the beams overlap. Expanded eyebox E decreases sensitivity to the position of a viewer’s eye for viewing the virtual image.

[0073] Out-coupling diffractive optics with refractive index variations along a single dimension can expand one dimension of the eyebox by replicating the individual angularly related beams in their direction of propagation along the waveguide between encounters with the out-coupling diffractive optic. In addition, out-coupling diffractive optics with refractive index variations along a second dimension can expand a second dimension of the eyebox and provide two-dimensional expansion of the eyebox. The refractive index variations along a first dimension of the out- coupling diffractive optic can be arranged to diffract a portion of each beam’s energy out of the image light guide upon each encounter therewith through a desired first order of diffraction, while another portion of the beam’s energy is preserved for further propagation in its original direction through a zero order of diffraction. The refractive index variations along a second dimension of the out-coupling diffractive optic can be arranged to diffract a portion of each beam’s energy upon each encounter therewith through a desired first order of diffraction in a direction angled relative to the beam’s original direction of propagation, while another portion of the beam’s energy is preserved for further propagation in its original direction through a zero order of diffraction.

[0074] Out-coupling diffractive optic ODO can be a reflective or transmissive-type diffraction grating arranged on second surface 314 of image light guide 310. However, like in-coupling diffractive optic IDO, out-coupling diffractive optic ODO can be located on, in, or engaged with first surface 312 or second surface 314 of image light guide 310 and be of a transmissive or reflective type in a combination that depends upon the direction through which image-bearing light WG is intended to exit image light guide 310.

[0075] As illustrated in FIG. 13, image light guide 310 may be arranged for expanding eyebox E in two dimensions, i.e., along both x- and y-axes of the intended image. To achieve a second dimension of beam expansion, in-coupling diffractive optic IDO, having grating vector kO, is oriented to diffract a portion of image-bearing light WI toward intermediate optic TO, having grating vector kl, which is oriented to diffract a portion of image-bearing light WG in a reflective mode toward out-coupling diffractive optic ODO. It should be appreciated that intermediate optic TO is an optional feature. Intermediate optic TO may be referred to herein as a turning grating or turning optic. In an embodiment, intermediate optic TO is a surface relief grating. In another embodiment, intermediate optic TO is a holographic optical element. Only a portion of imagebearing light WG is diffracted by each of multiple encounters with intermediate optic TO thereby laterally replicating each of the angularly related beams of image-bearing light WG approaching out-coupling diffractive optic ODO. Intermediate optic TO redirects image-bearing light WG toward out-coupling diffractive optic ODO for longitudinally replicating the angularly related beams of image-bearing light WG in a second dimension before exiting image light guide 310 asimage-bearing light WO. Grating vectors, such as the depicted grating vectors kO, kl, k2, extend in a direction that is normal to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optics and have a magnitude inverse to the period or pitch d (i.e., the on-center distance between grooves) of diffractive optics IDO, TO, ODO. In-coupling diffractive optic IDO, intermediate optic TO, and out-coupling diffractive optic ODO may each have a different period or pitch d.

[0076] With continued reference to FIG. 13, in-coupling diffractive optic IDO receives incoming image-bearing light WI containing a set of angularly related beams corresponding to individual pixels or equivalent locations within an image generated by image source 318. Image source 318, operable to generate a full range of angularly encoded beams for producing a virtual image, may be, but is not limited to, a real display together with focusing optics, a beam scanner for more directly setting the angles of the beams, or a combination such as a one-dimensional real display used with a scanner. Image source 318 will be described in greater detail below.

[0077] Image light guide 310 outputs an expanded set of angularly related beams in two dimensions of the image by providing multiple encounters of image-bearing light WG with both intermediate optic TO and out-coupling diffractive optic ODO in different orientations. In the original orientation of image light guide 310, intermediate grating TO provides beam expansion in the y-axis direction, and out-coupling diffractive optic ODO provides a similar beam expansion in the x-axis direction. The reflectivity characteristics and respective periods d of diffractive optics IDO, ODO, TO, together with the orientations of their respective grating vectors, provide for beam expansion in two dimensions while preserving the intended relationships among the angularly related beams of image-bearing light WI that are output from image light guide 310 as imagebearing light WO.

[0078] While image-bearing light WI input into image light guide 310 is encoded into a different set of angularly related beams by in-coupling diffractive optic IDO, the information required to reconstruct the image is preserved by accounting for the systematic effects of in-coupling diffractive optic IDO. Intermediate optic TO, located in an intermediate position between incoupling and out-coupling diffractive optics IDO, ODO, is typically arranged so that it does not induce any significant change on the encoding of image-bearing light WG. Out-coupling diffractive optic ODO is typically arranged in a symmetric fashion with respect to in-coupling diffractive optic IDO, e.g., including diffractive features sharing the same period. Similarly, the period of intermediate optic TO also typically matches the common period of in-coupling and out- coupling diffractive optics IDO, ODO. As illustrated in FIG. 13, grating vector kl of intermediate optic TO may be oriented at forty-five degrees (45°) with respect to the other grating vectors kO,k2 (all as undirected line segments). However, in an embodiment, grating vector kl of the intermediate optic TO is oriented at sixty degrees (60°) to grating vectors kO, k2 of in-coupling and out-coupling diffractive optics IDO, ODO in such a way that image-bearing light WG is turned one hundred and twenty degrees (120°). By orienting grating vector kl of intermediate optic TO at sixty degrees (60°) with respect to grating vectors kO, k2 of in-coupling and out- coupling diffractive optics IDO, ODO, grating vectors kO, k2 are also oriented at sixty degrees (60°) with respect to each other (again considered as undirected line segments). The three grating vectors kO, kl, k2 (as directed line segments) form an equilateral triangle, and sum to a zero-vector magnitude, which avoids asymmetric effects that could introduce unwanted aberrations including chromatic dispersion.

[0079] Image-bearing light WI that is diffracted into image light guide 310 is effectively encoded by in-coupling diffractive optic IDO, whether in-coupling diffractive optic IDO uses gratings, holograms, prisms, mirrors, or some other mechanism. Any reflection, refraction, and / or diffraction of light that takes place at in-coupling diffractive optic IDO must be correspondingly decoded by out-coupling diffractive optic ODO to re-form the virtual image that is presented to the viewer. Intermediate optic TO, placed at an intermediate position between in-coupling and out-coupling diffractive optics IDO, ODO, is typically designed and oriented so that it does not induce any change on the encoded light. Out-coupling diffractive optic ODO decodes imagebearing light WG into its original or desired form of angularly related beams that have been expanded to fill eyebox E.

[0080] Whether any symmetries are maintained or not among intermediate optic TO and incoupling and out-coupling diffractive optics IDO, ODO, or whether any change to the encoding of the angularly related beams of image-bearing light WI takes place along image light guide 310, intermediate optic TO and in-coupling and out-coupling diffractive optics IDO, ODO are related so that image-bearing light WO that is output from image light guide 310 preserves or otherwise maintains the original or desired form of image-bearing light WI for producing the intended virtual image.

[0081] The letter “R” represents the orientation of the virtual image that is visible to the viewer whose eye is in eyebox E. As shown, the orientation of the letter “R” in the represented virtual image matches the orientation of the letter “R” as encoded by image-bearing light WI. A change in the rotation about the z-axis or angular orientation of incoming image-bearing light WI with respect to the x-y plane causes a corresponding symmetric change in rotation or angular orientation of outgoing light from out-coupling diffractive optic ODO. From the aspect of image orientation, intermediate optic TO simply acts as a type of optical relay, providing expansion ofthe angularly encoded beams of image-bearing light WG along one axis (e.g., along the y-axis) of the image. Out-coupling diffractive optic ODO further expands the angularly encoded beams of image-bearing light WG along another axis (e.g., along the x-axis) of the image while maintaining the original orientation of the virtual image encoded by image-bearing light WI. As illustrated in FIG. 13, intermediate optic TO may be a slanted or square grating arranged on the front or back (i.e., first or second) surfaces of image light guide 310. Alternately, intermediate optic TO may be a blazed grating.

[0082] Referring again to FIG. 12, image source 318 includes at least one microLED assembly 10 and at least one projection lens 330. Projection lens 330 collimates output light from microLED assembly 10 to create an image of microLED display pixels at infinite focus (i.e., for imaging by eye). In an exemplary embodiment, projection lens 330 is spaced apart from microLED assembly 10 within image source 318 in direction DI. In an exemplary embodiment, image source 318 is spaced apart from surface 312 in direction D2. In an exemplary embodiment, image source 318 abuts against surface 312.

[0083] FIG. 14 is a top view of microLED display system 300. MicroLED display system 300 is substantially the same as microLED display system 300 shown in FIGS. 12-13 except it includes image source assembly 320 instead of image source 318. Image source assembly 320 comprises a plurality of image sources 318, for example, image sources 318A-318C, and X-cube prism 350. Image source 318A is arranged on a first side of X-cube prism 350 and optimized to emit light in a first color wavelength range, for example, red. Image source 318B is arranged on a second side of X-cube prism 350 and optimized to emit light in a second color wavelength range, for example, green. Image source 318C is arranged on a third side of X-cube prism 350 and optimized to emit light in a third color wavelength range, for example, blue. X-cube prism 350 is operatively arranged to combine the various color light from image sources 318 A- 318C to form a color image, and direct the color image to image light guide 310. As shown, each image source 318A-318C may include a respective projection or imaging lens located optically before the X-cube prism 350. In an exemplary embodiment, image source 318A is spaced apart from X-cube prism 350 in direction D3, image source 318B is spaced apart from X-cube prism 350 in direction D2, and image source 318C is spaced apart from X-cube prism 350 in direction D4. In an exemplary embodiment, X-cube prism 350 is spaced apart from surface 312 in direction D2. In an exemplary embodiment, X-cube prism 350 abuts against surface 312.

[0084] FIG. 15 is a top view of a microLED display system 300. MicroLED display system 300 is substantially the same as microLED display system 300 shown in FIGS. 12-13 except it includes image source assembly 322 instead of image source 318. Image source assembly 322 comprisesa plurality of microLED assemblies, for example, microLED assemblies 10A-10C, X-cube prism 350, and at least one projection lens 330. Projection lens 330 collimates output light from X-cube prism to create an image of microLED display pixels at infinite focus (i.e., for imaging by eye). MicroLED assembly 10A is arranged on a first side of X-cube prism 350 and optimized to emit light in a first color wavelength range, for example, red. MicroLED assembly 10B is arranged on a second side of X-cube prism 350 and optimized to emit light in a second color wavelength range, for example, green. MicroLED assembly 10C is arranged on a third side of X-cube prism 350 and optimized to emit light in a third color wavelength range, for example, blue. X-cube prism 350 is operatively arranged to combine the various color light from microLED assemblies 10 A- 10C to form a color image, and direct the color image to projection lens 330. In an exemplary embodiment, microLED assemblies 10A-10C abut against X-cube prism 350. In an exemplary embodiment, projection lens 330 is spaced apart from X-cube prism 350 within image source assembly 322 in direction DI . In an exemplary embodiment, image source assembly 322 is spaced apart from surface 312 in direction D2. In an exemplary embodiment, image source assembly 322 abuts against surface 312.

[0085] It should be appreciated that, in an exemplary embodiment, image source 318, image source assembly 320, image source assembly 322 may comprise one or more LEDs, organic LEDs (OLEDs), or microLEDs. In other examples, image source 318, image source assembly 320, image source assembly 322 may generate light in the following three primary color bands, for example, a green band having a wavelength in the range between 495 nm and 570 nm, a red band having a wavelength in the range between 620 nm and 750 nm, and a blue band having a wavelength in the range between 450 nm and 495 nm.

[0086] One or more features of the embodiments described herein may be combined to create additional embodiments which are not depicted. While various embodiments have been described in detail above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The embodiments described above are therefore to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

CLAIMS1. A micro light emitting diode (microLED) assembly (10), comprising: a package (20) including a volume (28); a microLED (40) arranged in the volume (28); and a lens (80) optically coupled to the microLED (40), wherein an immersion material (60) is arranged between the microLED (40) and the lens (80) provides the optical coupling and wherein the immersion material is a liquid.2 The microLED assembly (10) as recited in claim 1, wherein: the package further comprises a bottom surface (30) and a lateral surface (32); the volume (28) is bounded, at least in part, by the bottom surface (30) and the lateral surface (32); and the microLED (40) is secured to the bottom surface (30).3 The microLED assembly (10) as recited in claim 2, wherein the microLED (40) comprises: a transistor backplane (42) bonded to the bottom surface (30); and a light emitting frontplane (50) connected to the transistor backplane (42).4 The microLED assembly (10) as recited in claim 1, wherein: the package further comprises a first rear surface (22) and a first front surface (24); and the microLED (40) is spaced apart from the first front surface (24).5 The microLED assembly (10) as recited in claim 4, wherein the lens (80) comprises: a planar surface (82) connected to the package (20); and at least one curvilinear surface (84) extending from the planar surface (82) in a first direction (DI).6 The microLED assembly (10) as recited in claim 5, wherein the planar surface (82) is directly connected to the first front surface (24) of the package (20) and at least partially encloses volume (28).7 The microLED assembly (10) as recited in claim 5, further comprising a cover window (70 including:a second rear surface (72) connected to the first front surface (24); and a second front surface (74).

8. The microLED assembly (10) as recited in claim 7, wherein: the second rear surface (72) is directly connected to the first front surface (24) and at least partially encloses the volume (28); and the planar surface (82) is directly connected to the second front surface (74).9 The microLED assembly (10) as recited in claim 1, wherein the lens (80) is a half ball lens or a truncated half ball lens.10 The microLED assembly (10) as recited in claim 1, wherein the lens (80) is a diffractive lens or metalens.11 The microLED assembly (10) as recited in claim 1, wherein the lens (80) is a plano-convex lens12 The microLED assembly (10) as recited in claim 4, wherein the package (20) further comprises at least one port (34, 36) extending to the volume (28) from an outer surface (22, 24, 26 of the package (20).13 The microLED assembly (10) as recited in claim 12, wherein the package (20) comprises a first port (34) and a second port (36) extending from the first rear surface (22) to the volume (28 in a first direction (DI).14 The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) is sealed in the volume (28) by the lens (80) or a cover window (70).15 The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) comprises a silicone fluid.16 The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) comprises an oil.

17. The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) comprises an optical fluid.

18. The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) comprises glycerol.

19. The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) comprises a refractive index greater than or equal to 1.4 and less than or equal to 1.8.

20. The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) comprises an electrical resistivity of greater than 108ohm-cm.

21. The microLED assembly (10) as recited in claim 1, wherein the immersion material (60) comprises a freezing point of less than -10°C.

22. The microLED assembly (10) as recited in claim 1, wherein: the lens (80) comprises a first refractive index; the immersion material (60) comprises a second refractive index; and the absolute value of the difference between the first refractive index and the second refractive index is greater than 0.1.

23. The microLED assembly (10) as recited in claim 1 , wherein light emitted by the microLED assembly (10) travels from, in order, the microLED (40), through the immersion material (60), and then through the lens (80).

24. A micro light emitting diode (microLED) display system (300), comprising: an image source (318) arranged to emit image-bearing light, including: a projection lens (330); and at least one microLED assembly (10), comprising: a package (20) including a volume (28); a microLED (40) arranged in the volume (28); and a lens (80) optically coupled to the microLED (40), wherein an immersion material (60) is arranged between the microLED (40) and the lens (80) wherein the immersion material is a liquid; andan image light guide (310) including: an in-coupling diffractive optic (IDO) operable to couple the image-bearing light into the image light guide (310); and an out-coupling diffractive optic (ODO) operable to form a virtual image that is viewable from a viewer eyebox (E).

25. The microLED display system (300) as recited in claim 24, further comprising an X-cube prism (350) optically arranged between the at least one microLED assembly (10) and the projection lens (330).

Images