Low profile interconnect for light emitter

In some embodiments, an interconnect electrical connects a light emitter to wiring on a substrate. The interconnect may be deposited by 3D printing and lays flat on the light emitter and substrate. In some embodiments, the interconnect has a generally rectangular or oval cross-sectional profile and extends above the light emitter to a height of about 50 μm or less, or about 35 μm or less. This small height allows close spacing between an overlying optical structure and the light emitter, thereby providing high efficiency in the injection of light from the light emitter into the optical structure, such as a light pipe.

BACKGROUND

Field

The present disclosure relates to light sources and, more particularly, to light sources with light emitters mounted on substrates. In some embodiments, the light emitters may be light emitting diodes.

Description of the Related Art

Light emitters mounted on substrates, such as light emitting diodes mounted on circuit boards, are used as light sources to provide illumination in various electronic devices. The substrates may include wire bonds that connect the light emitters with wiring on the substrates, to provide power to the light emitters. As the specifications for modern devices change, e.g., as requirements for efficiency, robustness, and/or compactness increase, there is a continuing need to develop light sources that can meet the needs of these modern devices.

SUMMARY

In some embodiments, an illumination system is provided. The illumination system comprises a substrate comprising a substrate bond pad. A light emitter is attached to the substrate, and the light emitter comprises a light emitter bond pad. An electrical interconnect is over the light emitter. The electrical interconnect contacts the light emitter bond pad at one end of the electrical interconnect and contacts the substrate bond pad at an other end of the electrical interconnect. The cross-sectional shape of the electrical interconnect, as viewed in a plane traverse to an elongate axis of the electrical interconnect, has a width larger than a height. A maximum height of the electrical interconnect above the light emitter may be 50 μm or less in some embodiments. The electrical interconnect may conformally follow contours of the light emitter in some embodiments.

In some other embodiments, a method for making an illumination device is provided. The method comprises providing a light emitter, comprising a light emitter bond pad, over a substrate comprising a substrate bond pad. The method further comprises depositing an electrical interconnect over the light emitter and in contact with the light emitter bond pad and the substrate bond pad. Depositing the electrical interconnect may comprise 3D printing the electrical interconnect in some embodiments.

It will be appreciated that the drawings are provided to illustrate example embodiments and are not intended to limit the scope of the disclosure. Like reference numerals refer to like features throughout.

DETAILED DESCRIPTION

Light emitters may be coupled to overlying optical structures (e.g., light pipes) that receive light from the light emitters to, e.g., further transmit that light and/or to modify the light. It will be appreciated that the efficiency of the injection of light from the light emitter into the optical structures is strongly dependent on the distance separating the light emitter and the optical structure. Smaller separations provide higher efficiencies, with a higher percentage of the emitted light being injected into the optical structures. The impact of smaller separations can increase with decreases in the widths or transverse dimensions of the optical structures and light emitters; as a transverse dimension decreases, more power is lost around the edges by light missing the optical structure. For example, where the optical structure and light emitter dimensions in transverse directions are smaller than 1.5 mm, the impact of the separation on efficiency is readily apparent. Thus, the impact of the separation, between a light emitter and an optical structure that receives light from the light emitter, increases as the cross-sectional areas of the surfaces of the light emitter and optical structure decrease.

As noted above, power may be provided to light emitters using wire bonds. Conventional wire bonds, however, have been found to limit how closely overlying optical structures can be spaced from the light emitters.FIG. 1illustrates an example of a cross-sectional side view of a light source500having a wire bond502connecting a light emitter510to a bond pad520on a substrate530. An electrical contact540provides a second connection between the light emitter510and wiring (not shown) in the substrate530. It will be appreciated that the wire bond500and the electrical contact540are electrical interconnects and may function as cathodes and anodes for supplying power to the light emitter.

Wire bonds are typically metallic wires with circular cross sections. As illustrated, these wires may gently curve upwards and then downwards to the bond pad to, e.g., prevent breakage that may be caused by making sharp corners with the wires. The upward curvature adds to the height of a light source that includes the wire bond. In addition, the wire has been found to be undesirable for display systems, since it may block light from light emitter and form a shadow that may cause a visual artifact in a projected image. The wire bond may also limit how closely adjacent light emitters can be placed onto the substrate, as the wire bond must have a certain loop height above the chip and cannot curve downwards too sharply. In addition, an encapsulating material550may be formed around the wire bond502and light emitter510, to provide mechanical protection and electrical insulation for the wire bond502and the light emitter510. The encapsulating material550further adds to the height of the light source500, thereby spacing any optical structures from the light emitter510by at least the height of the encapsulating material550, which in turn has a height dictated by the wire bond502.

Advantageously, according to some embodiments, light emitters having exceptionally low profile electrical interconnects are provided. In some embodiments, the interconnects connect a light emitter to bond pads on a substrate. A single light source may include one, or two or more interconnects, each connected to bond pads. The interconnects may have a cross-sectional profile that, as viewed head on, has a width that is larger than a height, e.g., the profile may be generally rectangular or oval-shaped. Preferably, the interconnect is formed by deposition, e.g., by a printing process such as 3D printing, which forms a strip of material over the light emitter. It will be appreciated that the strip, as deposited, has a generally rectangular or oval-shaped cross-section. In some embodiments, a dielectric layer is formed on the light emitter and then the interconnect is deposited. Both the dielectric and the interconnect may be deposited by the same type of deposition, e.g., both may be deposited by 3D printing.

The deposited interconnect may conformally follow the contours of the underlying surface topology, e.g., the contours of the light emitter and any other structures on the substrate, and this topology may be assumed by the conformal dielectric layer, where such a dielectric layer is deposited. In some embodiments, both the interconnect and dielectric layer are strips of material. It will be appreciated that the substrates can include any material that can support electrical circuits, such as standard FR4, ceramic, metallic and combinations thereof.

Advantageously, the interconnect lays flat over the light emitter, thereby protruding only a small amount above the light emitter. In some embodiments, the interconnect connects to a bond pad on top of the light emitter and proximate the edge of light emitting area or outside of light emitting area, which can have advantages for reducing shadow-type artifacts in a projected image. In some embodiments, the interconnect extends above the light emitter to a height of about 50 μm or less, about 35 μm or less, about 25 μm or less, or about 20 μm or less. This small height allows close spacing between an overlying optical structure, e.g., light pipes or reflectors, and the light emitter, thereby providing high efficiency in the injection of light from the light emitter into the optical structure. In some embodiments, because the interconnect lays directly on an underlying material, such as on a deposited dielectric layer, the interconnect may be sufficiently mechanically and environmentally stable to omit use of an encapsulating material. This avoidance of the encapsulating material may provide advantages for simplifying manufacturing and reducing manufacturing costs, while also allowing a closer spacing of an overlying optical structure to the light emitter. In addition, directly forming the interconnect in contact with the substrate surface provides a more robust and shock and vibration-resistant interconnect than a thin bond wire suspended above the light emitter and substrate.

Reference will now be made to the drawings, in which like reference numerals refer to like parts throughout.

With reference now toFIG. 2A, an example is illustrated of a cross-sectional side view of a light source600having a light emitter610connected to a bond pad620on a substrate630by a low-profile interconnect640. As illustrated, the light emitter610may also have a bond pad650to which the interconnect640makes direct contact. Thus, the interconnect640makes an electrical connection between the bond pad620in the substrate630and the bond pad650on the light emitter610. In some embodiments, an electrical contact660under the light emitter610makes another electrical connection to the light emitter610. One of the interconnect640and the electrical contact660may function as an anode and the other of the interconnect640and the electrical contact660may function as a cathode to provide power to the light emitter610.

It will be appreciated that the bond pads620and650may be areas of conductive material on or in the light emitter610and substrate630, respectively, to which the interconnect640can make a stable electrical contact. In some embodiments, the bond pads620and650are deposits of material on the light emitter610or the substrate630. Preferably, the bond pads620and650are formed of metallic material. In some embodiments, the bond pad620may be part of wiring on the substrate630, such as wiring for providing power to the light emitter610and may also help to remove heat in some applications, and may have a larger width than the wiring. In some embodiments, the substrate630may be a printed circuit board. The wider interconnect640may have a lower height or thickness than a wire bond but actually help remove more heat than a wire bond due, e.g., to its larger area, which may allow the interconnect to function as a heat sink. This is advantageous as heat is detrimental to light emitter performance and lifespan.

In some embodiments, the light emitter610is a light emitting diode (LED) device, such as a LED chip. In some embodiments, the LED is formed by a semiconductor having p and n-doped regions that form a p-n junction that emits light upon the application of a voltage across the junction.

With continued reference toFIG. 2A, the interconnect640may be formed by a deposition process. In some embodiments, the deposition process may be a 3D printing process. Advantageously, 3D printing allows for the selective deposition of material at particular locations, and the deposition may be conformal to facilitate a low height. The 3D printing process may include various processes capable of depositing a continuous layer of conductive material. In some embodiments, the material is a metal. Non-limiting examples of metals include aluminum, gold, and copper. In some embodiments, the width and thickness of the interconnect can be varied along its length for desired mechanical fit or electrical or thermal performance.

Non-limiting examples of 3D printing processes include material extrusion and powder bed fusion. In material extrusion, a supply of material (e.g., a metal) is melted and flowed out of an opening (e.g., an opening in a nozzle) to deposit the interconnect material on a surface. In some embodiments, multiple lines of material may be deposited directly neighboring one another, at the side of another row of material, to increase the width of the deposited interconnect640and to increase the amount of deposited material as desired. In addition or alternatively, the lines may be deposited on top of one another to increase the thickness of the deposited interconnect640.

In powder bed fusion, a loose bed of material (e.g., a bed of metal powder or particles) is selectively heated by a heat source to form a continuous mass of material at the locations of the applied heat, while the unheated portions of the bed remain in powder or particle form and may be subsequently removed. In some embodiments, the heat source may be any heat source capable of supplying sufficient localized energy to sinter or melt the material, thereby forming a solid mass of material to define the interconnect640. Examples of heat sources include devices that can project a beam of high-energy radiation or particles to the bed of material. For example, the heat sources may be lasers and/or electron beams. In some embodiments, the high-energy beam (e.g., a beam with sufficient energy to sinter or melt particles in the bed of material) may be scanned over the bed of material, thereby sintering or melting the particles together, to form a continuous line of material. In addition, the high-energy beam may be further scanned across the bed of material to form neighboring lines, to extend the width of the interconnect640to increase the amount of deposited material. In some embodiments, another bed of material may be deposited over the sintered or melted material, and then exposed to the high-energy beam to increase the height of the deposited interconnect either generally, or at specific locations (such as to extend the interconnect up a side of a wall). In addition to the processes above, other 3D printing processes for depositing dielectric materials may also be used to form the dielectric layer670.

It will be appreciated while referred to as lines of material, the material deposited by 3D printing extends linearly in some embodiments, but may form a curve or make a turn in some other embodiments, as viewed in a top down view. In addition, as seem inFIG. 2A, the interconnect640is deposited conformally on the light emitter610and the substrate630; that is, as seem in a side view, the profile of the interconnect640may conform to and track the profile of the underlying light emitter610and substrate30.

As noted herein, the interconnect640may supply power to the light emitter. It will be appreciated that the resistance of the interconnect640will decrease with increases in the head-on cross-sectional area of the interconnect640(that is, the cross-sectional area of the interconnect640transverse to the length dimension of the interconnect640extending from the bond pad620to the bond pad650, which may include the cross-sectional area taken along the plane2B-2B). As a result, the number of lines of material deposited to form the interconnect640is preferably chosen to provide a sufficiently large cross-sectional area to provide power to the light emitter610without undue resistance or heat generation.

In some embodiments, the interconnect640may have an elongated cross-section.FIG. 2Billustrates an example of a cross-sectional view of the illumination system ofFIG. 2A, as seem in a cross-section taken along the plane2B-2B ofFIG. 2A. The plane2B-2B is traverse to an elongate axis of the interconnect640(e.g., traverse to the axis along which the interconnect640extends from the bond pad620to the bond pad650); the view illustrated inFIG. 2Bmay be considered to be the view of the interconnect640as seem head on. As illustrated, the interconnect640has a width W and a height H. In some embodiments, W is larger than H, which can have advantages for providing a low-profile interconnect, while also allowing sufficient material to achieve a desirably low resistance. In some embodiments, W is larger than H by a factor of about 1.5 or more, 50 or more, or 100 or more.

It will be appreciated that the light emitter610and/or the substrate630may have conductive materials within them or on them. For example, where the light emitter is a LED chip, the light emitter610may be formed of a semiconductor die, which can conduct electricity. In some embodiments, the substrate670may include conductive features, such as wire traces or a bond pad for the electrical contact660that extends beyond the light emitter660. For example, this arrangement may be found in some ceramic circuit boards. To prevent undesired contact or shorting of the interconnect640with other conductive features, a dielectric layer may be formed along the path of the interconnect640before depositing that interconnect640.FIG. 3illustrates an example of a cross-sectional side view of the light source600having a dielectric layer670underlying a low-profile interconnect640. In some embodiments, the dielectric layer670may be a strip of material that traces the path of the interconnect640, and that is wider than and extends beyond the sides of the interconnect640. In some other embodiments, the dielectric layer670may be a blanket layer of dielectric overlies portions of the substrate630and the light emitter610.

In some embodiments, the dielectric layer670may be deposited by 3D printing. The 3D printing process for depositing the dielectric layer670may include various processes capable of depositing a continuous layer of dielectric material. Non-limiting examples of dielectric materials include epoxies, resins, glues, plastics, polycarbonates, and other polymer based materials.

Non-limiting examples of 3D printing processes include material extrusion, powder bed fusion, material jetting, binder jetting. Material extrusion and powder bed fusion may be similar to that described above for deposition of the interconnect640, except that a dielectric material may be deposited instead of a conductive material. Material jetting may be performed by jetting droplets or liquid streams of material out of a nozzle and then hardening that material by the application of energy (e.g., heat and/or light). Binder jetting may be performed by applying a powder on a surface and jetting droplets or liquid streams of binder material out of a nozzle on the powder to bind the powder together. In addition to the processes above, other 3D printing processes for depositing dielectric materials may also be used to form the dielectric layer670.

It will be appreciated that the dielectric layer670may extend over parts of one or both of the bonds pads620and650.FIG. 4illustrates an example of a cross-sectional side view of the light source600having the dielectric layer670underlying the interconnect650and also partly overlying the bond pads620and650. As illustrated, an end670aof the dielectric layer670overlies a portion of the bond pad620and an end670bof the dielectric layer670overlies a portion of the bond pad650. In some embodiments, the dielectric layer670lies conformally over the substrate630, the light emitter610, and the bond pads620and/or650. In turn, the interconnect640conformally follows the contours of the light emitter610and the bond pads620and650. As illustrated, the interconnect640may directly contact the dielectric layer670, in addition to directly contacting the bond pads620and650. In some embodiments, the dielectric layer may be transparent or partly transparent to the light emitted by the light emitter610and thus cover all or portions of the light emitter without significantly blocking the emitted light.

The low profile of the interconnect640allows small spacing between the light emitter610and an overlying structure.FIG. 5illustrates an example of a cross-sectional side view of the light source600having an optical structure680over the light emitter610. In some embodiments, the optical structure680is a light collection structure such as a light pipe. The light emitter610is configured to inject light into the optical structure680through a gap690. In some embodiments, the height of the gap690, or the distance separating the optical structure680from the light emitter610, is about 150 μm or less, about 50 μm or less, about 25 μm or less, or about 20 μm or less. In some embodiments, the light emitter610may be exposed, with a gap690, filled with air, separating the light emitter610from the optical structure680.

In some other embodiments, a material other than air may fill the gap690. For example, a transparent adhesive or resin may fill the gap. Preferably, the material filling the gap may be formed of a material with a refractive index that substantially matches the refractive index of the material of the optical structure680, where the optical structure680is a light pipe.

It will be appreciated that the light pipe is formed of an optically transmissive material and may be used to transmit light. Non-limiting examples of optically transmissive materials include poly(methyl methacrylate) (PMMA) and other acrylics, glass, polycarbonate, or any other optical grade polymeric material. Light injected into the light pipe680may propagate through the light pipe by total internal reflection (TIR). In some embodiments, TIR is facilitated by providing a low refractive index material at the sides of the light pipe. For example, the low index material may be air or a cladding layer having a refractive index that is less than the refractive index of the light pipe by 0.1 or more.

In some embodiments, the optical structure680is a reflective light collection system. For example, the light collection system may include a reflector such as a circular or eleciptical cone or a Compound Parabolic Concentrator (CPC).

It will be appreciated that that the light emitter610and interconnect640may be encapsulated using an optically transmissive encapsulating material.FIG. 6illustrates an example of a cross-sectional side view of the light source600ofFIG. 5having an encapsulating material700over the light emitter610and the optical structure680over the encapsulating material. As shown, the gap690may be filled by the encapsulating material700and the optical structure680may be disposed immediately over and in contact with the encapsulating material700. The encapsulating material700may protect the light emitter610and the interconnect640. Non-limiting examples of encapsulating materials include silicone and epoxy resin. In some embodiments, a gap690created by the thickness of the encapsulating material690between the light emitter610and the optical structure680separates the light emitter640and the optical structure680by about 50 μm or less, about 40 μm or less, or about 10 μm or less or in contact with

The small separation between the light emitter640and the optical structure680has been found to significantly impact the power efficiency of light emitters.FIG. 7is a plot showing the power efficiency of a light pipe as a function of distance between the light pipe and a light emitter. The power efficiency is on the y-axis and the distance between the light pipe and the light emitter is on the x-axis. The power efficiency may be understood to be the percentage of the total amount of outputted light from the light emitter which is captured and subsequently outputted by the light pipe. Notably, at distances of 50 μm or less, the power efficiency is 90% or higher, while the power efficiency falls down steeply at distances of 50 μm or more and, more particularly, 100 μm or more. As result, maintaining a gap690between the light emitter610and the optical structure680at distances of about 50 μm or less, about 35 μm or less, about 25 μm or less, or about 20 μm or less are expected to provide exceptionally high power efficiency.

In the example above, the transverse dimensions of the light pipe are about 400×400 um. A light emitter for such a light pipe may fall in the range of about 10×10 um to about 700×700 um. If the light emitter is too small, insufficient light is generated to begin with. If the light emitter is too large and a large proportion of the light misses the light pipe or reflector system, although the large size makes the system more robust to misalignment. As the size of the light collector get smaller then the gap must be less to keep the efficiency of the system.

Referring both toFIGS. 5 and 6, as examples, the illustrated light source600may be similar to the configuration of the light source illustratedFIG. 4. In some other embodiments, the light source600may have any of the configurations discussed herein, e.g., such as the configurations illustrated inFIGS. 2A-3.

Example Display Systems

It will be appreciated that the low-profile interconnects may be utilized in various illumination applications in which a low profile over the light emitter is desired. As discussed therein, the low profile can provide tight spacing between the light emitter and an overlying optical structure, such as a light pipe. This tight spacing can allow for highly efficient transfer of light from the light emitter into the light pipe. Another advantage is that, by eliminating the wire bond, the interconnect can be more robust against shock and vibration as well as environmental concerns. In addition, these interconnects may allow for the light sources to be placed closer together which can make the optical system smaller and lighter weight, for a given level of output. Such high efficiency, robustness, and small size may advantageously be utilized in display devices, to increase the brightness and portability and/or reduce the power usage of the displays.

In some embodiments, the light emitters may be used to illuminate augmented or virtual reality display systems. In some embodiments, these display systems may by wearable and portable, with present images on multiple depth planes, with light sources required for each depth plane. The high efficiency provided with the low-profile interconnects can advantageously facilitate the portability of the display system, e.g., by reducing power requirements and the increasing battery life of power sources and reducing the size for the display system. These concerns may be particularly important for optical systems that use multiple light sources for illumination.

With reference toFIG. 8, an augmented reality scene1is depicted. It will be appreciated that modern computing and display technologies have facilitated the development of systems for so called “virtual reality” or “augmented reality” experiences, wherein digitally reproduced images or portions thereof are presented to a user in a manner wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. A mixed reality, or “MR”, scenario is a type of AR scenario and typically involves virtual objects that are integrated into, and responsive to, the natural world. For example, an MR scenario may include AR image content that appears to be blocked by or is otherwise perceived to interact with objects in the real world.

FIG. 8shows an example of an AR scene in which a user of an AR technology sees a real-world park-like setting1100featuring people, trees, buildings in the background, and a concrete platform1120. In addition to these items, the user of the AR technology also perceives that he “sees” a robot statue1110standing upon the real-world platform1120, and a cartoon-like avatar character1130flying by which seems to be a personification of a bumble bee, even though these elements1130,1110do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce a VR or AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements.

FIG. 9illustrates an example of wearable display system80. The display system80includes a display62, and various mechanical and electronic modules and systems to support the functioning of that display62. The display62may be coupled to a frame64, which is wearable by a display system user or viewer60and which is configured to position the display62in front of the eyes of the user60. The display62may be considered eyewear in some embodiments. In some embodiments, a speaker66is coupled to the frame64and positioned adjacent the ear canal of the user60(in some embodiments, another speaker, not shown, is positioned adjacent the other ear canal of the user to provide for stereo/shapeable sound control). In some embodiments, the display system may also include one or more microphones67or other devices to detect sound. In some embodiments, the microphone is configured to allow the user to provide inputs or commands to the system80(e.g., the selection of voice menu commands, natural language questions, etc.) and/or may allow audio communication with other persons (e.g., with other users of similar display systems).

With continued reference toFIG. 9, the display62is operatively coupled68, such as by a wired lead or wireless connectivity, to a local data processing module70which may be mounted in a variety of configurations, such as fixedly attached to the frame64, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removably attached to the user60(e.g., in a backpack-style configuration, in a belt-coupling style configuration). The local processing and data module70may comprise a hardware processor, as well as digital memory, such as non-volatile memory (e.g., flash memory or hard disk drives), both of which may be utilized to assist in the processing, caching, and storage of data. The data include data a) captured from sensors (which may be, e.g., operatively coupled to the frame64or otherwise attached to the user60), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and/or gyros; and/or b) acquired and/or processed using remote processing module72and/or remote data repository74, possibly for passage to the display62after such processing or retrieval. The local processing and data module70may be operatively coupled by communication links76,78, such as via a wired or wireless communication links, to the remote processing module72and remote data repository74such that these remote modules72,74are operatively coupled to each other and available as resources to the local processing and data module70. In some embodiments, the local processing and data module70may include one or more of the image capture devices, microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, and/or gyros. In some other embodiments, one or more of these sensors may be attached to the frame64, or may be standalone structures that communicates with the location processing and data module70by wired or wireless communication pathways.

With continued reference toFIG. 9, in some embodiments, the remote processing module72may comprise one or more processors configured to analyze and process data and/or image information. In some embodiments, the remote data repository74may comprise a digital data storage facility, which may be available through the internet or other networking configuration in a “cloud” resource configuration. In some embodiments, the remote data repository74may include one or more remote servers, which provide information, e.g., information for generating augmented reality content, to the local processing and data module70and/or the remote processing module72. In some embodiments, all data is stored and all computations are performed in the local processing and data module, allowing fully autonomous use from a remote module.

The perception of an image as being “three-dimensional” or “3-D” may be achieved by providing slightly different presentations of the image to each eye of the viewer.FIG. 10illustrates a conventional display system for simulating three-dimensional imagery for a user. Two distinct images5,7—one for each eye4,6—are outputted to the user. The images5,7are spaced from the eyes4,6by a distance10along an optical or z-axis parallel to the line of sight of the viewer. The images5,7are flat and the eyes4,6may focus on the images by assuming a single accommodated state. Such systems rely on the human visual system to combine the images5,7to provide a perception of depth for the combined image.

It will be appreciated, however, that the human visual system is more complicated and providing a realistic perception of depth is more challenging. For example, many viewers of conventional “3-D” display systems find such systems to be uncomfortable or may not perceive a sense of depth at all. Without being limited by theory, it is believed that viewers of an object may perceive the object as being “three-dimensional” due to a combination of vergence and accommodation. Vergence movements (i.e., rolling movements of the pupils toward or away from each other to converge the lines of sight of the eyes to fixate upon an object) of the two eyes relative to each other are closely associated with focusing (or “accommodation”) of the lenses of the eyes. Under normal conditions, a change in vergence of the eyes when shifting attention from one object to another object at a different distance will automatically cause a matching change in the focus of the lenses of the eyes, or accommodation of the eyes, under a relationship known as the “accommodation-vergence reflex.” Likewise, a change in accommodation will trigger a matching change in vergence, under normal conditions. As noted herein, many stereoscopic or “3-D” display systems display a scene using slightly different presentations (and, so, slightly different images) to each eye such that a three-dimensional perspective is perceived by the human visual system. Such systems are uncomfortable for many viewers, however, since they, among other things, simply provide a different presentations of a scene, but with the eyes viewing all the image information at a single accommodated state, and work against the “accommodation-vergence reflex.” Display systems that provide a better match between accommodation and vergence may form more realistic and comfortable simulations of three-dimensional imagery.

FIG. 11illustrates aspects of an approach for simulating three-dimensional imagery using multiple depth planes. Objects at various distances from eyes4,6on the z-axis are accommodated by the eyes4,6so that those objects are in focus. The eyes (4and6) assume particular accommodated states to bring into focus objects at different distances along the z-axis. Consequently, a particular accommodated state may be said to be associated with a particular one of depth planes14, with has an associated focal distance, such that objects or parts of objects in a particular depth plane are in focus when the eye is in the accommodated state for that depth plane. In some embodiments, three-dimensional imagery may be simulated by providing different presentations of an image for each of the eyes4,6, and also by providing different presentations of the image corresponding to each of the depth planes. While shown as being separate for clarity of illustration, it will be appreciated that the fields of view of the eyes4,6may overlap, for example, as distance along the z-axis increases. It will addition, while shown as flat for ease of illustration, it will be appreciated that the contours of a depth plane may be curved in physical space, such that all features in a depth plane are in focus with the eye in a particular accommodated state.

The distance between an object and the eye4or6can also change the amount of divergence of light from that object, as viewed by that eye.FIGS. 12A-12Cillustrates relationships between distance and the divergence of light rays. The distance between the object and the eye4is represented by, in order of decreasing distance, R1, R2, and R3. As shown inFIGS. 12A-12C, the light rays become more divergent as distance to the object decreases. As distance increases, the light rays become more collimated. Stated another way, it may be said that the light field produced by a point (the object or a part of the object) has a spherical wavefront curvature, which is a function of how far away the point is from the eye of the user. The curvature increases with decreasing distance between the object and the eye4. Consequently, at different depth planes, the degree of divergence of light rays is also different, with the degree of divergence increasing with decreasing distance between depth planes and the viewer's eye4. While only a single eye4is illustrated for clarity of illustration inFIGS. 12A-12Cand other figures herein, it will be appreciated that the discussions regarding eye4may be applied to both eyes4and6of a viewer.

Without being limited by theory, it is believed that the human eye typically can interpret a finite number of depth planes to provide depth perception. Consequently, a highly believable simulation of perceived depth may be achieved by providing, to the eye, different presentations of an image corresponding to each of these limited number of depth planes. The different presentations may be separately focused by the viewer's eyes, thereby helping to provide the user with depth cues based on the accommodation of the eye required to bring into focus different image features for the scene located on different depth plane and/or based on observing different image features on different depth planes being out of focus.

FIG. 13illustrates an example of a waveguide stack for outputting image information to a user. A display system1000includes a stack of waveguides, or stacked waveguide assembly,178that may be utilized to provide three-dimensional perception to the eye/brain using a plurality of waveguides182,184,186,188,190. In some embodiments, the display system1000is the system80ofFIG. 9, withFIG. 13schematically showing some parts of that system80in greater detail. For example, the waveguide assembly178may be part of the display62ofFIG. 9. It will be appreciated that the display system1000may be considered a light field display in some embodiments.

With continued reference toFIG. 13, the waveguide assembly178may also include a plurality of features198,196,194,192between the waveguides. In some embodiments, the features198,196,194,192may be lens. The waveguides182,184,186,188,190and/or the plurality of lenses198,196,194,192may be configured to send image information to the eye with various levels of wavefront curvature or light ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image injection devices200,202,204,206,208may function as a source of light for the waveguides and may be utilized to inject image information into the waveguides182,184,186,188,190, each of which may be configured, as described herein, to distribute incoming light across each respective waveguide, for output toward the eye4. These light sources may be made more efficient and may be spaced closer together using the interconnects disclosed herein. By using different sources the light sources themselves act to switch depth planes by switching on or off the illumination for each depth plane, as desired. Light exits an output surface300,302,304,306,308of the image injection devices200,202,204,206,208and is injected into a corresponding input surface382,384,386,388,390of the waveguides182,184,186,188,190. In some embodiments, the each of the input surfaces382,384,386,388,390may be an edge of a corresponding waveguide, or may be part of a major surface of the corresponding waveguide (that is, one of the waveguide surfaces directly facing the world144or the viewer's eye4). In some embodiments, a single beam of light (e.g. a collimated beam) may be injected into each waveguide to output an entire field of cloned collimated beams that are directed toward the eye4at particular angles (and amounts of divergence) corresponding to the depth plane associated with a particular waveguide. In some embodiments, a single one of the image injection devices200,202,204,206,208may be associated with and inject light into a plurality (e.g., three) of the waveguides182,184,186,188,190.

In some embodiments, the image injection devices200,202,204,206,208are discrete displays that each produce image information for injection into a corresponding waveguide182,184,186,188,190, respectively. In some other embodiments, the image injection devices200,202,204,206,208are the output ends of a single multiplexed display which may, e.g., pipe image information via one or more optical conduits (such as fiber optic cables) to each of the image injection devices200,202,204,206,208. It will be appreciated that the image information provided by the image injection devices200,202,204,206,208may include light of different wavelengths, or colors (e.g., different component colors, as discussed herein).

In some embodiments, the light injected into the waveguides182,184,186,188,190is provided by a light output module209a, which may include a light source, such as the light source600(FIGS. 2A-4). The light from the light output module209amay be modified by a light modulator209b, e.g., a spatial light modulator. The light modulator209bmay be configured to change the perceived intensity of the light injected into the waveguides182,184,186,188,190. Examples of spatial light modulators include liquid crystal displays (LCD), including a liquid crystal on silicon (LCOS), and a digital light processing (DLP) displays. While not illustrated, it will be appreciated that various other optical structures (e.g., polarizing beam splitters) may be provided between the light output module209aand the light modulator209bto direct the propagation of light as desired to facilitate the propagation of light from the light output module209A to the light modulator209B and from the light modulator209B to the waveguides182,184,186,188,190.

In some embodiments, the light output module209amay include multiple light collectors680, e.g., light pipes or reflectors, as shown inFIG. 15. Each light collector680may be configured to output light (e.g., by transmitting and/or reflecting the light) into the light modulator209b(FIG. 13). These light pipes or reflectors680may each be optically coupled with one or more associated light sources600arranged in patterns on the substrate630(e.g., a printed circuit board) and the low-profile interconnects according to some embodiments may advantageously be employed to provide electrical connections in these light sources600. In some embodiments, the light emitters610(FIG. 5) of the light sources600may be smaller than 1.5×1.5 mm, or smaller than 800×800 um or smaller than 300×300 um in some embodiments. As discussed herein, for these smaller sized light emitters, a given distance between the collectors680and the light emitter has a more significant impact on the amount of light collected by the light collector680then for larger light emitters. Also, where multiple light sources600are employed, the impact of the efficiency of light collection caused by the closeness between the light collectors680and the light emitters of each light source600are magnified, since the multiple light sources600will see the impact of low efficiency light collection in the aggregate. Advantageously, light sources600with the low-profile interconnects disclosed herein can provide a higher light collection efficiency, which may be particularly beneficial where multiple light sources600are employed. The light output module209amay also include a housing and baffles (not shown) for, respectively, enclosing and preventing light leakage between light collectors680and between light sources600.

With reference again toFIG. 13, a controller210controls the operation of one or more of the stacked waveguide assembly178, including operation of the image injection devices200,202,204,206,208, the light emitter209a, and the light modular209b. In some embodiments, the controller210is part of the local data processing module70. The controller210includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides182,184,186,188,190according to, e.g., any of the various schemes disclosed herein. In some embodiments, the controller may be a single integral device, or a distributed system connected by wired or wireless communication channels. The controller210may be part of the processing modules70or72(FIG. 9) in some embodiments.

With continued reference toFIG. 13, the waveguides182,184,186,188,190may be configured to propagate light within each respective waveguide by total internal reflection (TIR). The waveguides182,184,186,188,190may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and edges extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides182,184,186,188,190may each include outcoupling optical elements282,284,286,288,290that are configured to extract light out of a waveguide by redirecting the light, propagating within each respective waveguide, out of the waveguide to output image information to the eye4. Extracted light may also be referred to as outcoupled light and the outcoupling optical elements light may also be referred to light extracting optical elements. An extracted beam of light is outputted by the waveguide at locations at which the light propagating in the waveguide strikes a light extracting optical element. The outcoupling optical elements282,284,286,288,290may, for example, be gratings, including diffractive optical features, as discussed further herein. While illustrated disposed at the bottom major surfaces of the waveguides182,184,186,188,190for ease of description and drawing clarity, in some embodiments, the outcoupling optical elements282,284,286,288,290may be disposed at the top and/or bottom major surfaces, and/or may be disposed directly in the volume of the waveguides182,184,186,188,190, as discussed further herein. In some embodiments, the outcoupling optical elements282,284,286,288,290may be formed in a layer of material that is attached to a transparent substrate to form the waveguides182,184,186,188,190. In some other embodiments, the waveguides182,184,186,188,190may be a monolithic piece of material and the outcoupling optical elements282,284,286,288,290may be formed on a surface and/or in the interior of that piece of material.

With continued reference toFIG. 13, as discussed herein, each waveguide182,184,186,188,190is configured to output light to form an image corresponding to a particular depth plane. For example, the waveguide182nearest the eye may be configured to deliver collimated light, as injected into such waveguide182, to the eye4. The collimated light may be representative of the optical infinity focal plane. The next waveguide up184may be configured to send out collimated light which passes through the first lens192(e.g., a negative lens) before it can reach the eye4; such first lens192may be configured to create a slight convex wavefront curvature so that the eye/brain interprets light coming from that next waveguide up184as coming from a first focal plane closer inward toward the eye4from optical infinity. Similarly, the third up waveguide186passes its output light through both the first192and second194lenses before reaching the eye4; the combined optical power of the first192and second194lenses may be configured to create another incremental amount of wavefront curvature so that the eye/brain interprets light coming from the third waveguide186as coming from a second focal plane that is even closer inward toward the person from optical infinity than was light from the next waveguide up184.

The other waveguide layers188,190and lenses196,198are similarly configured, with the highest waveguide190in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power representative of the closest focal plane to the person. To compensate for the stack of lenses198,196,194,192when viewing/interpreting light coming from the world144on the other side of the stacked waveguide assembly178, a compensating lens layer180may be disposed at the top of the stack to compensate for the aggregate power of the lens stack198,196,194,192below. Such a configuration provides as many perceived focal planes as there are available waveguide/lens pairings. Both the outcoupling optical elements of the waveguides and the focusing aspects of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, either or both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides182,184,186,188,190may have the same associated depth plane. For example, multiple waveguides182,184,186,188,190may be configured to output images set to the same depth plane, or multiple subsets of the waveguides182,184,186,188,190may be configured to output images set to the same plurality of depth planes, with one set for each depth plane. This can provide advantages for forming a tiled image to provide an expanded field of view at those depth planes.

With continued reference toFIG. 13, the outcoupling optical elements282,284,286,288,290may be configured to both redirect light out of their respective waveguides and to output this light with the appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides having different associated depth planes may have different configurations of outcoupling optical elements282,284,286,288,290, which output light with a different amount of divergence depending on the associated depth plane. In some embodiments, the light extracting optical elements282,284,286,288,290may be volumetric or surface features, which may be configured to output light at specific angles. For example, the light extracting optical elements282,284,286,288,290may be volume holograms, surface holograms, and/or diffraction gratings. In some embodiments, the features198,196,194,192may not be lenses; rather, they may simply be spacers (e.g., cladding layers and/or structures for forming air gaps).

In some embodiments, the outcoupling optical elements282,284,286,288,290are diffractive features that form a diffraction pattern, or “diffractive optical element” (also referred to herein as a “DOE”). Preferably, the DOE's have a sufficiently low diffraction efficiency so that only a portion of the light of the beam is deflected away toward the eye4with each intersection of the DOE, while the rest continues to move through a waveguide via total internal reflection. The light carrying the image information is thus divided into a number of related exit beams that exit the waveguide at a multiplicity of locations and the result is a fairly uniform pattern of exit emission toward the eye4for this particular collimated beam bouncing around within a waveguide.

In some embodiments, one or more DOEs may be switchable between “on” states in which they actively diffract, and “off” states in which they do not significantly diffract. For instance, a switchable DOE may comprise a layer of polymer dispersed liquid crystal, in which microdroplets comprise a diffraction pattern in a host medium, and the refractive index of the microdroplets can be switched to substantially match the refractive index of the host material (in which case the pattern does not appreciably diffract incident light) or the microdroplet can be switched to an index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

FIG. 14shows an example of exit beams outputted by a waveguide. One waveguide is illustrated, but it will be appreciated that other waveguides in the waveguide assembly178may function similarly, where the waveguide assembly178includes multiple waveguides. Light400is injected into the waveguide182at the input surface382of the waveguide182and propagates within the waveguide182by TIR. At points where the light400impinges on the DOE282, a portion of the light exits the waveguide as exit beams402. The exit beams402are illustrated as substantially parallel but, as discussed herein, they may also be redirected to propagate to the eye4at an angle (e.g., forming divergent exit beams), depending on the depth plane associated with the waveguide182. It will be appreciated that substantially parallel exit beams may be indicative of a waveguide with outcoupling optical elements that outcouple light to form images that appear to be set on a depth plane at a large distance (e.g., optical infinity) from the eye4. Other waveguides or other sets of outcoupling optical elements may output an exit beam pattern that is more divergent, which would require the eye4to accommodate to a closer distance to bring it into focus on the retina and would be interpreted by the brain as light from a distance closer to the eye4than optical infinity.

Various example embodiments of the invention are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the invention. Various changes may be made to the invention described and equivalents may be substituted without departing from the spirit and scope of the invention. For example, while advantageously utilized with AR displays that provide images across multiple depth planes, the augmented reality content disclosed herein may also be displayed by systems that provide images on a single depth plane. In addition, while advantageously applied as a light source for display systems, the light sources disclosed herein may be utilized in other applications where close spacing of the light emitter to other structures is desired.

In some embodiments, with reference toFIGS. 2A-6, the electrical contact660may be omitted and a second contact (not shown) to the light emitter610may be made using a second interconnect (not shown) similar to the interconnect640. For example, the second interconnect may be deposited over the substrate to contact a second light emitter bond pad (not shown) on an exposed surface of the light emitter610(e.g., on an upward-facing surface of the light emitter, opposite from the bond pad650) and a second substrate bond pad (not shown) on the substrate630. The second interconnect may be deposited by similar methods as the first interconnect640and, in some embodiments, a dielectric layer (not shown) similar to the dielectric layer670may be formed before depositing the second interconnect.

Many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. Further, as will be appreciated by those with skill in the art that each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present inventions. All such modifications are intended to be within the scope of claims associated with this disclosure.

Example aspects of the invention, together with details regarding material selection and manufacture have been set forth above. As for other details of the present invention, these may be appreciated in connection with the above-referenced patents and publications as well as generally known or appreciated by those with skill in the art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts as commonly or logically employed.

In addition, though the invention has been described in reference to several examples optionally incorporating various features, the invention is not to be limited to that which is described or indicated as contemplated with respect to each variation of the invention. Various changes may be made to the invention described and equivalents (whether recited herein or not included for the sake of some brevity) may be substituted without departing from the spirit and scope of the invention. In addition, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention.

The breadth of the present invention is not to be limited to the examples provided and/or the subject specification, but rather only by the scope of claim language associated with this disclosure.