PATENT DOCUMENT

Publication Number: US-11774644-B1
Application Number: US-202016902091-A
Country: US
Kind Code: B1

Title: Electronic devices with image transport layers having light absorbing material

Abstract:
An electronic device may have a housing with a display. A protective display cover layer for the display may have an image transport layer formed from fibers or Anderson localization material. The image transport layer may include light absorbing material. Light absorbing material may be incorporated as an additive into a component of the image transport layer such as the binder layer of a coherent fiber bundle or the cladding of fibers in the image transport layer. The image transport layer may also be formed from fibers with a light absorbing layer formed in addition to a transparent cladding. The image transport layer may be formed from Anderson localization material that has light absorbing material. Fibers for the image transport layer may be extruded with light absorbing portions. A polymer preform having light absorbing material may be drawn to form fibers for the image transport layer.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 an array of pixels configured to display an image; and 
 an image transport layer having an input surface and an output surface, wherein the image transport layer is configured to transport the image from the input surface to the output surface and wherein the image transport layer includes a plurality of fibers that each comprise:
 a core that extends along a length; and 
 a light absorbing cladding formed around the core, wherein the light absorbing cladding comprises a transparent polymer and elongated strips of light absorbing material that extend parallel to the length and wherein the elongated strips are distributed around a perimeter of the transparent polymer. 
 
 
     
     
       2. The electronic device defined in  claim 1 , wherein the light absorbing material is a light absorbing polymer material. 
     
     
       3. The electronic device defined in  claim 1 , wherein the light absorbing cladding has an inner surface and an opposing outer surface, wherein the inner surface is adjacent to the core, and wherein the elongated strips of light absorbing material are formed at the outer surface of the light absorbing cladding. 
     
     
       4. The electronic device defined in  claim 1 , wherein each strip of light absorbing material is contained within a respective transparent tube. 
     
     
       5. The electronic device defined in  claim 1 , wherein the elongated strips of light absorbing material are black fibers. 
     
     
       6. The electronic device defined in  claim 1 , wherein the elongated strips of light absorbing material are gray fibers. 
     
     
       7. The electronic device defined in  claim 1 , wherein the elongated strips of light absorbing material each have a first cross-sectional area that is more than 5 times smaller than a second cross-sectional area of each fiber of the plurality of fibers. 
     
     
       8. An electronic device comprising:
 an array of pixels configured to display an image; and 
 an image transport layer having an input surface and an output surface, wherein the image transport layer is configured to transport the image from the input surface to the output surface and wherein the image transport layer includes a plurality of fibers that each comprise:
 a core; and 
 a light absorbing cladding formed around the core, wherein the light absorbing cladding comprises a transparent portion, wherein the transparent portion is formed from a fluoropolymer and has an outer surface, and wherein the light absorbing cladding further comprises a coating of fluorine-doped light absorbing dye on the outer surface of the transparent portion. 
 
 
     
     
       9. The electronic device defined in  claim 8 , wherein the fluoropolymer is polyvinylidene fluoride. 
     
     
       10. The electronic device defined in  claim 8 , wherein the fluoropolymer is a terpolymer of ethyelene, tetrafluoroethylene, and hexafluoropropylene. 
     
     
       11. An electronic device comprising:
 an array of pixels configured to display an image; and 
 an image transport layer having an input surface and an output surface, wherein the image transport layer is configured to transport the image from the input surface to the output surface and wherein the image transport layer includes a plurality of fibers that each comprise:
 a core; and 
 a light absorbing cladding formed around the core, wherein the plurality of fibers includes a first fiber at an edge of the image transport layer and a second fiber at a center of the image transport layer, wherein the first fiber includes light absorbing material having a first absorbance magnitude, and wherein the second fiber includes light absorbing material having a second absorbance magnitude that is less than the first absorbance magnitude. 
 
 
     
     
       12. The electronic device defined in  claim 8 , wherein the fluoropolymer is a terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride.

Description:
This application claims the benefit of provisional patent application No. 62/893,540, filed Aug. 29, 2019, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to electronic devices, and, more particularly, to display cover layers for electronic devices. 
     BACKGROUND 
     Electronic devices may have displays. Displays have arrays of pixels for displaying images for a user. To prevent damage to the pixels, the pixels can be covered with a transparent display cover layer. If care is not taken, however, the inclusion of a display cover layer into an electronic device may cause the device to have larger inactive border regions than desired or may introduce undesired image distortion. 
     SUMMARY 
     An electronic device may have a housing. A display may be mounted in the housing. A protective display cover layer may be formed over the display. During operation, images on the display may be viewed through the protective display cover layer. 
     The protective display cover layer may have an image transport layer formed from fibers or Anderson localization material. The image transport layer may guide and expand image light from the display and thereby expand the effective size of images on the display. The expanded image size helps cover peripheral housing structures and minimizes the size of display borders. 
     The image transport layer may include light absorbing material. The light absorbing material may absorb unguided light in the image transport layer to increase contrast and reduce blur. Light absorbing material may be incorporated as an additive into a component of the image transport layer. For example, a light absorbing additive may be incorporated into the binder of a coherent fiber bundle or into the cladding of fibers in the image transport layer. The image transport layer may also be formed from fibers with a dedicated light absorbing layer in addition to a transparent cladding. The image transport layer may be formed from Anderson localization material that has light absorbing material. 
     To form the image transport layer, an extruder may form fiber bundles that each include a respective plurality of fibers distributed in binder material. The extruder may have hoppers that each contain raw material for a respective portion of the fibers. Light absorbing additive may be mixed into one of the hoppers with another raw material. Alternatively, the extruder may have a dedicated hopper for the light absorbing material. In some cases, fibers may be formed by drawing down a polymer preform. The polymer preform may have first, second, and third cladding portions. Light absorbing material such as pre-drawn light absorbing fibers may be incorporated into one of the cladding portions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a side view of an illustrative electronic device with an image transport layer in accordance with an embodiment. 
         FIG.  2    is a top view of an illustrative image transport layer in accordance with an embodiment. 
         FIG.  3    is a top view of a portion of an image transport layer in accordance with an embodiment. 
         FIG.  4    is a cross-sectional side view of a portion of an image transport layer in accordance with an embodiment. 
         FIG.  5    is a top view of illustrative fibers for an image transport layer with light absorbing material incorporated into the binder layer in accordance with an embodiment. 
         FIG.  6    is a top view of an illustrative fiber for an image transport layer with light absorbing material incorporated into the cladding in accordance with an embodiment. 
         FIG.  7    is a top view of an illustrative fiber for an image transport layer with a light absorbing layer formed around a transparent cladding in accordance with an embodiment. 
         FIG.  8    is a top view of an illustrative fiber for an image transport layer with a light absorbing layer interposed between first and second transparent claddings in accordance with an embodiment. 
         FIG.  9    is a top view of an illustrative fiber for an image transport layer with strips of light absorbing material integrated into the cladding in accordance with an embodiment. 
         FIG.  10    is a cross-sectional view of illustrative Anderson localization material in accordance with an embodiment. 
         FIG.  11    is a cross-sectional view of illustrative Anderson localization material that includes light absorbing material incorporated into low-index filaments in accordance with an embodiment. 
         FIG.  12    is a side view of an illustrative extruder with a hopper that contains both raw material for a binder layer and light absorbing additive in accordance with an embodiment. 
         FIG.  13    is a side view of an illustrative extruder with a hopper that contains both raw material for a cladding layer and light absorbing additive in accordance with an embodiment. 
         FIG.  14    is a side view of an illustrative extruder with a dedicated hopper that contains light absorbing material in accordance with an embodiment. 
         FIG.  15    is a side view of illustrative fiber drawing equipment such as a draw tower in accordance with an embodiment. 
         FIG.  16    is a top view of an illustrative polymer preform that includes pre-drawn light absorbing fibers in a middle cladding portion in accordance with an embodiment. 
         FIG.  17    is a top view of an illustrative polymer preform that includes pre-drawn light absorbing fibers in an outer cladding portion in accordance with an embodiment. 
         FIG.  18    is a top view of an illustrative fiber that is formed by drawing the polymer preform of  FIG.  16    in accordance with an embodiment. 
         FIG.  19    is a top view of an illustrative fiber that is formed by drawing the polymer preform of  FIG.  17    in accordance with an embodiment. 
         FIG.  20    is a flow chart of illustrative steps involved in forming an image transport layer for an electronic device display in accordance with an embodiment. 
         FIG.  21    is a graph showing various profiles for the amount of light absorbing material in each fiber versus position across the image transport layer in accordance with an embodiment. 
         FIG.  22 A  is a top view of an illustrative polymer preform that includes protected light absorbing fibers in an outer cladding portion in accordance with an embodiment. 
         FIG.  22 B  is a top view of an illustrative fiber that is formed by drawing the polymer preform of  FIG.  22 A  in accordance with an embodiment. 
         FIG.  23 A  is a top view of an illustrative polymer preform that includes light absorbing fibers between transparent outer cladding portions in accordance with an embodiment. 
         FIG.  23 B  is a top view of an illustrative fiber that is formed by drawing the polymer preform of  FIG.  23 A  in accordance with an embodiment. 
         FIG.  24 A  is a top view of an illustrative polymer preform that includes a ring of light absorbing material between transparent outer cladding portions in accordance with an embodiment. 
         FIG.  24 B  is a top view of an illustrative fiber that is formed by drawing the polymer preform of  FIG.  24 A  in accordance with an embodiment. 
         FIG.  25 A  is a top view of an illustrative fiber surrounded by a binder material that includes a doped light absorbing additive in accordance with an embodiment. 
         FIG.  25 B  is a top view of the illustrative fiber of  FIG.  25 A  after heat causes the doped light absorbing additive to preferentially aggregate on an outer surface of the cladding of the fiber in accordance with an embodiment. 
         FIG.  26    is a flow chart of illustrative steps involved in using a doped light absorbing additive in a binder material to form a light absorbing cladding in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device may have a display. The display may have an array of pixels for creating an image. The image may pass through a protective display cover layer that overlaps the array of pixels. To minimize display borders, the display cover layer may include an image transport layer formed from a coherent fiber bundle or Anderson localization material. The image transport layer may receive an image from a display at an input surface and may provide the image to a corresponding output surface for viewing by a user. The image transport layer may have a shape that helps expand the effective size of the image without imparting undesired distortion to the image and/or may have other configurations. 
     In one illustrative configuration, which may sometimes be described herein as an example, an image transport layer for the display in an electronic device is formed from a fiber optic plate that contains a coherent fiber bundle. In another illustrative configuration, an image transport layer for the display in an electronic device is formed from Anderson localization material. 
     A cross-sectional side view of a portion of an illustrative electronic device with a display cover layer that includes an image transport layer is shown in  FIG.  1   . In the example of  FIG.  1   , device  10  is a portable device such as a cellular telephone, wristwatch, or tablet computer. Other types of devices may have display cover layers with image transport layers, if desired. 
     Device  10  includes a housing such as housing  12 . Housing  12  may be formed from polymer, metal, glass, crystalline material such as sapphire, ceramic, fabric, fibers, fiber composite material, natural materials such as wood and cotton, other materials, and/or combinations of such materials. Housing  12  may be configured to form housing walls. The housing walls may enclose one or more interior regions such as interior region  24  and may separate interior region  24  from exterior region  22 . 
     Electrical components  18  may be mounted in interior region  24 . Electrical components  18  may include integrated circuits, discrete components, light-emitting components, sensors, and/or other circuits and may, if desired, be interconnected using signal paths in one or more printed circuits such as printed circuit  20 . If desired, one or more portions of the housing walls may be transparent (e.g., so that light associated with an image on a display or other light-emitting or light-detecting component can pass between interior region  24  and exterior region  22 ). 
     Electrical components  18  may include control circuitry. The control circuitry may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in the control circuitry may be used to control the operation of device  10 . For example, the processing circuitry may use sensors and other input-output circuitry to gather input and to provide output and/or to transmit signals to external equipment. The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. The control circuitry may include wired and/or wireless communications circuitry (e.g., antennas and associated radio-frequency transceiver circuitry such as cellular telephone communications circuitry, wireless local area network communications circuitry, etc.). The communications circuitry of the control circuitry may allow device  10  to communicate with other electronic devices. For example, the control circuitry (e.g., communications circuitry in the control circuitry) may be used to allow wired and/or wireless control commands and other communications to be conveyed between devices such as cellular telephones, tablet computers, laptop computers, desktop computers, head-mounted devices, handheld controllers, wristwatch devices, other wearable devices, keyboards, computer mice, remote controls, speakers, accessory displays, accessory cameras, and/or other electronic devices. Wireless communications circuitry may, for example, wirelessly transmit control signals and other information to external equipment in response to receiving user input or other input from sensors or other devices in components  18 . 
     Input-output circuitry in components  18  of device  10  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. The input-output circuitry may include input devices that gather user input and other input and may include output devices that supply visual output, audible output, or other output. 
     Output may be provided using light-emitting diodes (e.g., crystalline semiconductor light-emitting diodes for status indicators and/or displays, organic light-emitting diodes in displays and other components), lasers, and other light-emitting devices, audio output devices (e.g., tone generators and/or speakers), haptic output devices (e.g., vibrators, electromagnetic actuators, piezoelectric actuators, and/or other equipment that supplies a user with haptic output), and other output devices. 
     The input-output circuitry of device  10  (e.g., the input-output circuitry of components  18 ) may include sensors. Sensors for device  10  may include force sensors (e.g., strain gauges, capacitive force sensors, resistive force sensors, etc.), audio sensors such as microphones, touch and/or proximity sensors such as capacitive sensors (e.g., a two-dimensional capacitive touch sensor integrated into a display, a two-dimensional capacitive touch sensor and/or a two-dimensional force sensor overlapping a display, and/or a touch sensor or force sensor that forms a button, trackpad, or other input device not associated with a display), and other sensors. Touch sensors for a display or for other touch components may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. If desired, a display may have a force sensor for gathering force input (e.g., a two-dimensional force sensor may be used in gathering force input on a display). 
     If desired, the sensors may include optical sensors such as optical sensors that emit and detect light, ultrasonic sensors, optical touch sensors, optical proximity sensors, and/or other touch sensors and/or proximity sensors, monochromatic and color ambient light sensors, image sensors, fingerprint sensors, temperature sensors, sensors for measuring three-dimensional non-contact gestures (“air gestures”), pressure sensors, sensors for detecting position, orientation, and/or motion (e.g., accelerometers, magnetic sensors such as compass sensors, gyroscopes, and/or inertial measurement units that contain some or all of these sensors), health sensors, radio-frequency sensors (e.g., sensors that gather position information, three-dimensional radio-frequency images, and/or other information using radar principals or other radio-frequency sensing), depth sensors (e.g., structured light sensors and/or depth sensors based on stereo imaging devices), optical sensors such as self-mixing sensors and light detection and ranging (lidar) sensors that gather time-of-flight measurements, humidity sensors, moisture sensors, gaze tracking sensors, three-dimensional sensors (e.g., time-of-flight image sensors, pairs of two-dimensional image sensors that gather three-dimensional images using binocular vision, three-dimensional structured light sensors that emit an array of infrared light beams or other structured light using arrays of lasers or other light emitters and associated optical components and that capture images of the spots created as the beams illuminate target objects, and/or other three-dimensional image sensors), facial recognition sensors based on three-dimensional image sensors, and/or other sensors. 
     In some configurations, components  18  may include mechanical devices for gathering input (e.g., buttons, joysticks, scrolling wheels, key pads with movable keys, keyboards with movable keys, and other devices for gathering user input). During operation, device  10  may use sensors and/or other input-output devices in components  18  to gather user input (e.g., buttons may be used to gather button press input, touch and/or force sensors overlapping displays can be used for gathering user touch screen input and/or force input, touch pads and/or force sensors may be used in gathering touch and/or force input, microphones may be used for gathering audio input, etc.). The control circuitry of device  10  can then take action based on this gathered information (e.g., by transmitting the information over a wired or wireless path to external equipment, by supplying a user with output using a haptic output device, visual output device, an audio component, or other input-output device in housing  12 , etc.). 
     If desired, electronic device  10  may include a battery or other energy storage device, connector ports for supporting wired communications with ancillary equipment and for receiving wired power, and other circuitry. In some configurations, device  10  may serve as an accessory and/or may include a wired and/or wireless accessory (e.g., a keyboard, computer mouse, remote control, trackpad, etc.). 
     Device  10  may include one or more displays. The displays may, for example, include an organic light-emitting diode display, a liquid crystal display, a display having an array of pixels formed from respective light-emitting diodes (e.g., a pixel array having pixels with crystalline light-emitting diodes formed from respective light-emitting diode dies such as micro-light-emitting diode dies), and/or other displays. The displays may include rigid display structures and/or may be flexible displays. For example, a light-emitting diode display may be sufficiently flexible to be bent. Displays for device  10  may have pixel arrays for displaying images for a user. Each pixel array (which may sometimes be referred to as a display panel, display substrate, or display) may be mounted under a transparent display cover layer that helps to protect the pixel array. In the example of  FIG.  1   , pixel array (display)  14  is mounted under image transport layer  16 . Optional additional layers (e.g., transparent layers of glass, crystalline material such as sapphire, etc.) may be stacked above and/or below layer  16 . Layer  16  and these additional layers may serve as a protective display cover layer (and may sometimes be referred to as forming a transparent portion of the housing for device  10 ). The configuration of  FIG.  1    in which a display cover layer for device  10  is formed from layer  16  is illustrative. 
     During operation, the pixels of display  14  produce image light that passes through optical structures  16 F in layer  16  for viewing by a user such as viewer  28  who is viewing device  10  in direction  26  (e.g., a user who is viewing device  10  straight on in a direction parallel to the surface normal of a planar central portion of layer  16  on front face F, a user who is viewing device  10  at an off-axis viewing angle such as at a 45° angle to the surface normal of a planar central portion of layer  16 , or a user who is viewing device  10  in other directions). Structures  16 F may be optical fibers (e.g., in scenarios in which image transport layer  16  is a coherent fiber bundle) or other elongated optical features. For example, structures  16 F may be filaments that have different refractive index values in scenarios in which image transport layer  16  is a layer of Anderson localization material. Structures  16 F may be referred to as fibers  16 F, filaments  16 F, etc. 
     Optical structures  16 F of image transport layer  16  allow an image produced by an array of pixels in a flat or curved display to be transferred from an input surface of a first shape at a first location to an output surface with a curved cross-sectional profile, compound curvature, or other desired second shape at a second location. The image transport layer may therefore move the location of an image and may optionally change the shape of the surface on which the image is presented. 
     Device  10  may have four peripheral edges and a rectangular footprint when viewed in direction  26  or may have other suitable shapes. To help minimize the size of inactive display borders as a user is viewing front face F of device  10  as shown in  FIG.  1   , the shapes of fibers  16 F along the rectangular periphery of plate  16  may be deformed outwardly as shown in  FIG.  1   . The deformed shapes of fibers  16 F help distribute image light laterally outwards in the X-Y plane so that the effective size of display  14  is enlarged and the image produced by display  14  covers some or all of the sidewalls of housing  12  when the image on front face F is being viewed by viewer  28 . For example, the bent shapes of fibers  16 F may help shift portions of the displayed image laterally outward in the X-Y plane along the edges and corners of device  10  to block the sidewall portions of housing  12  from view. In some arrangements, the portions of fibers  16 F at the outermost surface of layer  16  are oriented parallel or nearly parallel with viewing direction  26  and the Z axis of  FIG.  1   , which helps ensure that some or all of the light that has passed through plate  16  will travel in the Z direction and be viewable by viewer  28 . 
     Layer  16  may be formed from any suitable material such as polymer, glass, crystalline material such as sapphire, transparent ceramic, and/or other materials. Examples in which layer  16  is formed from polymer are sometimes described herein as an example. The polymer materials used in forming may be formed from glassy polymers such as polymethylmethacrylate (PMMA), polyester, or other amorphous polymers and/or may be formed from semicrystalline polymers such as fluoropolymers (e.g., THV or PVDF). 
     A top view of an image transport layer is shown in  FIG.  2   . As shown, the image transport layer may have a central portion  42 . Central portion  42  may have fibers that are not bent and may sometimes be referred to as an unformed portion or unbent portion of the image transport layer. The unformed portion of the image transport layer may be surrounded by a peripheral portion  44  of the image transport layer in which the fibers are bent (sometimes referred to as a formed portion or bent portion). As shown in the top view of  FIG.  2   , portion  44  may extend in a ring around portion  42  (e.g., portion  44  may laterally surround portion  42 ). Portion  44  may have fibers that are bent in order to hide an inactive border area of the display. 
     As shown in  FIG.  2   , the image transport may have a rectangular footprint with rounded corners when viewed from above. The rounded corners may be bent downwards (e.g., in the negative Z-direction away from the viewer and towards the display panel). The output surface of the image transport layer may have compound curvature in the rounded corner regions. 
     Image transport layer  16  may convey light from an input surface to an output surface of arbitrary shape. Ideally, each optical structure of the image transport layer would convey light in an ordered manner without any cross-talk between optical structures. However, in practice there may be challenges in preventing cross-talk and other undesired light emissions. For example, highly angled light from display  14  may not be properly guided by optical structures  16 F, resulting in improper translation of the display light between the input surface of the image transport layer and the output surface of the image transport layer. Light that is initially properly guided by optical structures  16 F may be susceptible to exiting the optical structures  16 F at bent portions of the optical structures. Additionally, ambient light may enter the image transport layer through the output surface and may reduce contrast in the displayed image. 
     To mitigate the presence of ‘unguided’ or otherwise undesired light, image transport layer  16  may include light absorbing material. The light absorbing material may sometimes be referred to as an electromagnetic absorber (EMA). There are many ways to incorporate light absorbing material into an image transport layer. The image transport layer may include light absorbing material in embodiments where the image transport layer is formed from a coherent fiber bundle or Anderson localization material. 
     First, image transport layers that are formed from fibers and that include light absorbing material will be discussed. Fibers used to form image transport layer  16  may have any suitable configuration. A cross-sectional view of fiber optic plate  16  in an illustrative arrangement in which fibers  52  have multiple layers of material is shown in  FIG.  3   . As shown in  FIG.  3   , fibers  52  may each have a core such as core  54 . Cores  54  and the other structures of image transport layer  16  may be formed from transparent materials such as polymer, glass, crystalline material such as sapphire, and/or other transparent materials. In an illustrative configuration, which may sometimes be described herein as an example, image transport layer  16  includes polymer fibers. 
     Fiber cores  54  may be formed from polymer of a first refractive index and may be surrounded by cladding  56  (e.g., polymer) of a second, lower refractive index. The difference in refractive index between cores  54  and cladding  56  may be greater than 0.1, greater than 0.2, greater than 0.3, between 0.2 and 0.4, etc. This arrangement allows fibers  52  to guide light in accordance with the principal of total internal reflection. Binder material  58  may hold fibers  52  together to form image transport layer  16  (fiber optic plate  16 ). The fractional cross-sectional area occupied by core  54  may be between 65% and 85%, between 60% and 75%, greater than 60%, greater than 65%, greater than 70%, or another desired value. The fractional cross-sectional area occupied by cladding  56  may be between 2% and 10%, between 1% and 20%, greater than 5%, less than 20%, less than 15%, less than 10%, or another desired value. The fractional cross-sectional area occupied by binder material  58  may be between 2% and 10%, between 1% and 20%, greater than 5%, less than 20%, less than 15%, less than 10%, or another desired value. 
     The diameter of core  54  may be 5-15 microns or other suitable size (e.g., at least 3 microns, at least 7 microns, 10 microns, at least 15 microns, less than 20 microns, less than 14 microns, etc.). The thickness of cladding  56  may be 0.5 microns, at least 0.1 microns, at least 0.4 microns, less than 2 microns, less than 0.9 microns, or other suitable thickness. If desired, fibers  52  may contain more layers, fewer layers, layers arranged in different orders, and/or may have other configurations. 
       FIG.  4    is a cross-sectional side view of fibers that may be used to form an image transport layer (e.g., the fibers of  FIG.  3   ). As shown, fibers  52  include cores  54  surrounded by cladding  56 . Binder  58  is interposed between adjacent fibers  52  (e.g., between claddings  56  of adjacent fibers). Fibers  52  are used to guide light (e.g., from display  14  in  FIG.  1   ). Light ray  60 - 1  shows an example of light being guided by a fiber. The index of refraction difference between cores  54  and cladding  56  allows fibers  52  to guide light  60 - 1  in accordance with the principal of total internal reflection. 
     As shown in  FIG.  4   , binder  58  may also guide light via total internal reflection. The difference in refractive index between binder  58  and cladding  56  may be greater than 0.01, greater than 0.05, greater than 0.1, greater than 0.2, greater than 0.3, between 0.2 and 0.4, etc. Having a refractive index difference between binder  58  and cladding  56  allows the portions of binder  58  between fibers  52  to serve as ‘supplemental cores’ that guide light in a similar fashion to cores  54  of fibers  52 . Light ray  60 - 2  shows an example of light being guided by binder  58  between fibers  52  in accordance with the principle of total internal reflection. 
     Light rays  60 - 1  and  60 - 2  may be examples of ‘guided’ light that is desirably conveyed from the input surface of layer  16  to the output surface of layer  16 . In general, it may be desirable to maximize the transmission of this type of light to improve the efficiency of the display and minimize blur. In contrast, it may be desirable to minimize the transmission of unguided light that is not guided by fiber cores  54  or binder  58 . Light rays  60 - 3  and  60 - 4  show examples of unguided light. As shown, light ray  60 - 3  may enter image transport layer  16  at the input surface at a high angle. Due to the high angle of incidence, the light ray may pass through the core-cladding interface of fiber  52  (instead of undergoing total internal reflection at the core-cladding interface as with light ray  60 - 1 ). Light ray  60 - 3  may pass through image transport layer  16  in an unguided fashion and may ultimately be emitted from the output surface of the image transport layer at a location that does not match the proper location in the displayed image. Similarly, light ray  60 - 4  may be ambient light that enters image transport layer  16  through the output surface of the image transport layer. Light ray  60 - 4  may pass through the image transport layer (from output surface to input surface), reflect off of the surface of display  14 , and pass through the image transport layer (from input surface to output surface) where it is emitted from the image transport layer. The paths of light  60 - 1 ,  60 - 2 ,  60 - 3 , and  60 - 4  depicted in  FIG.  4    are merely illustrative. In practice, there may be refraction at the interfaces between different components (e.g., light  60 - 3  and  60 - 4  may be refracted while passing in an unguided manner through the image transport layer), but changes of direction due to refraction have been omitted from  FIG.  4    for simplicity of the drawing. 
     It may be desirable to maximize transmission of certain types of light (e.g., guided light  60 - 1  and  60 - 2 ) but minimize transmission of other types of light (e.g., unguided light  60 - 3  and  60 - 4 ). The examples in  FIG.  4    are merely illustrative. It may be desirable to mitigate transmission of other types of light than those shown in  FIG.  4   . For example, ambient light may enter and be guided by cores  54 , cladding  56 , and/or binder  58 . Ideally, this ambient light would be absorbed and not emitted from the output surface of the image transport layer. 
     Light absorbing material may be incorporated into image transport layer  16  to absorb light and prevent transmission of undesired types of light. The more light absorbing material included in the image transport layer, the more the undesired light may be absorbed. However, the light properly guided by cores  54  or binder  58  may also, undesirably be absorbed. Therefore, the amount and absorbance of light absorbing material incorporated into the image transport layer may be selected to balance the mitigation of undesired light transmissions with ensuring satisfactory transmission of desired light transmissions. 
     There are many ways to incorporate light absorbing material into an image transport layer formed from fibers.  FIG.  5    is a top view of illustrative fibers that have light absorbing material incorporated into the binder material. The fibers in  FIG.  5    may have a similar structure to those in  FIGS.  3  and  4   , with each fiber  52  having a core  54  and cladding  56 . Binder  58  (sometimes referred to as binder layer  58 , binder material  58 , etc.) may hold together the fibers  52 . In  FIG.  5   , a light absorbing material  62  is incorporated into binder layer  58 . The light absorbing material  62  may be black pigment, black dye, or other light absorbing material that absorbs and blocks light (e.g., carbon black based material, carbon nanotubes, graphite nanoplatelets, etc.). 
     In  FIG.  5   , light absorbing material  62  (sometimes referred to as EMA  62 , dye  62 , pigment  62 , etc.) is incorporated as an additive into binder  58 . Unlike cladding  56 , which is coated on and surrounds the core  54 , binder  58  fills the interstitial space between the fibers. Binder  58  may be formed from a transparent polymer. With the additive included, binder layer  58  in  FIG.  5    may be gray (e.g., partially light absorbing). The EMA additive may be evenly distributed throughout the binder layer such that the binder layer has a uniform color (e.g., a uniform gray binder layer). 
     As previously mentioned, binder  58  may guide light from display  14  from the input surface of the image transport layer to the output surface of the image transport layer (e.g., the binder may serve as a supplemental core). Therefore, incorporating additive  62  into binder  58  may undesirably lower the transmission of this guided light. The additive may instead be incorporated into the cladding to avoid this issue. 
       FIG.  6    is a top view of an illustrative fiber that has light absorbing material incorporated into a cladding. Fiber  52  has a core  54  and cladding  56 . Binder  58  may hold together fiber  52  with other neighboring fibers having the same structure. In  FIG.  6   , a light absorbing material  62  is incorporated into cladding  56 . The light absorbing material  62  may be black pigment, black dye, or other light absorbing material that absorbs and blocks light. Cladding  56  may be formed from a transparent polymer. With the additive included, cladding  56  in  FIG.  6    may be gray (e.g., partially light absorbing). The EMA additive may be evenly distributed throughout the cladding such that the cladding has a uniform color (e.g., a uniform gray cladding). 
     In the arrangement of  FIG.  6   , core  54  may have a diameter  66  and cladding  56  may have a thickness  68 . Diameter  66  may be 5-15 microns at least 3 microns, at least 7 microns, 10 microns, 8-12 microns, at least 15 microns, less than 20 microns, less than 14 microns, etc. Thickness  68  may be less than 1 micron, less than 2 microns, greater than 0.1 micron, between 0.2 and 1.0 microns, etc. The refractive index of core  54  may be greater than 1.6, between 1.6 and 1.7, between 1.63 and 1.67, greater than 1.5, less than 1.7, etc. The refractive index of cladding  56  may be less than 1.4, between 1.3 and 1.4, between 1.33 and 1.37, etc. The refractive index of binder  58  may be greater than 1.5, greater than 1.55, between 1.5 and 1.65, between 1.5 and 1.6, between 1.55 and 1.6, etc. 
     In  FIGS.  5  and  6   , light absorbing material is incorporated as an additive into binder  58  or cladding  56 . These examples are merely illustrative. In another possible arrangement, a dedicated light absorbing layer may be incorporated into each fiber.  FIGS.  7  and  8    show arrangements of this type. 
       FIG.  7    is a top view of an illustrative fiber that has a dedicated light absorbing layer formed around a cladding. As shown in  FIG.  7   , fiber  52  has a core  54  and cladding  56 . Binder  58  may hold together fiber  52  with other neighboring fibers having the same structure. Fiber  52  also includes light absorbing layer  64 . Light absorbing layer  64  may include black pigment, black dye, or other light absorbing material that absorbs and blocks light (e.g., carbon black based material, carbon nanotubes, graphite nanoplatelets, etc.). Light absorbing layer  64  may sometimes be referred to as light absorbing cladding layer  64  or light absorbing cladding  64 . Light absorbing cladding  64  may include a light absorbing additive incorporated into a transparent polymer or may be formed from a light absorbing polymer (e.g., a gray or black polymer). 
     Light absorbing layer  64  in  FIG.  7    may desirably mitigate transmission of certain types of light, but may undesirably mitigate transmission of guided light in binder layer  58 .  FIG.  8    is a top view of an illustrative fiber that has a dedicated light absorbing layer formed between two claddings to prevent absorption of light that is desirably guided through binder  58 . As shown in  FIG.  8   , fiber  52  has a core  54 , cladding  56 - 1 , light absorbing layer  64  (light absorbing cladding  64 ), and cladding  56 - 2 . Binder  58  may hold together fiber  52  with other neighboring fibers having the same structure. Light absorbing layer  64  may include black pigment, black dye, or other light absorbing material that absorbs and blocks light. Light absorbing layer  64  may include a light absorbing additive incorporated into a transparent polymer or may be formed from a light absorbing polymer (e.g., a gray or black polymer). 
     In  FIG.  8   , light absorbing layer  64  is interposed between first and second claddings  56 - 1  and  56 - 2 . Consequently, light guided within binder layer  58  by total internal reflection will be less likely to be absorbed by light absorbing layer  64  (because the light will reflect off of cladding  56 - 2  before reaching light absorbing layer  64 ). In the arrangement of  FIG.  8   , core  54  may have a diameter  66  that is 5-15 microns, at least 3 microns, at least 7 microns, 10 microns, 8-12 microns, at least 15 microns, less than 20 microns, less than 14 microns, etc. Cladding  56 - 1  may have a thickness that is less than 1 micron, less than 2 microns, greater than 0.1 micron, between 0.2 and 1.0 microns, between 0.2 and 0.5 microns, less than 0.5 microns, etc. Light absorbing layer  64  may have a thickness that is less than 1 micron, less than 2 microns, greater than 0.01 micron, less than 0.5 microns, less than 0.3 microns, less than 0.2 microns, between 0.05 and 0.2 microns, etc. Cladding  56 - 2  may have a thickness that is less than 1 micron, less than 2 microns, greater than 0.01 micron, less than 0.5 microns, less than 0.3 microns, less than 0.2 microns, between 0.05 and 0.2 microns, etc. 
       FIG.  9    shows another possible arrangement for a fiber with light absorbing material. As shown in  FIG.  9   , fiber  52  has a core  54  and cladding  56 . Binder  58  may hold together fiber  52  with other neighboring fibers having the same structure. Fiber  52  also includes light absorbing material  70 . In  FIG.  9   , light absorbing material  70  may be gray or black fibers that are formed on an outer surface of cladding  56 . The light absorbing fibers  70  may extend along the length of each fiber  52 , effectively forming gray or black strips running along the length of fiber  52 . Any number of light absorbing fibers  70  may be incorporated into each fiber  52 . Having more light absorbing fibers will increase the overall absorption of stray light within the image transport layer. Light absorbing fibers  70  may sometimes be referred to as light absorbing filaments  70  and may have cross-sectional areas that are smaller than the total cross-sectional area of fibers  52  (e.g., more than 5 times smaller, more than 10 times smaller, more than 20 times smaller, etc.). 
     Because light absorbing material  70  is formed at the outer surface of cladding  56  (e.g., at the interface with binder  58 ), the light absorbing material is unlikely to absorb light that is being guided through core  54  of the fiber. Stray light passing through the image transport layer may be absorbed by the light absorbing material  70 . 
     As shown above, cladding for a fiber may include one or more layers between a fiber core and binder that holds the fibers together. The cladding may be coated on the fiber core and extend around the perimeter of the fiber core. If the cladding includes multiple layers, each layer may be referred to as a sublayer of the cladding or each layer may be referred to as a respective cladding. In some cases (as in  FIG.  6   ), the cladding may be formed from a single light absorbing layer that directly contacts the core. In other cases (as in  FIG.  7   ), the cladding may include a transparent layer that directly contacts the core and a light absorbing layer that is coated on the transparent layer. In general, the cladding may include any desired number of layers. 
     Image transport layer  16  may also be formed from Anderson localization material. Anderson localization material is characterized by transversely random refractive index features (e.g., higher index regions and lower index regions or regions of three or more or four or more different respective refractive indices) with a lateral size of about 300-500 nm, at least 100 nm, at least 700 nm, at least 1 micron, less than 5 microns, less than 1.5 microns, two wavelengths, or other suitable lateral size that are configured to exhibit two-dimensional transverse Anderson localization of light (e.g., the light output from the display of device  10 ). These refractive index variations are longitudinally invariant along the direction of light propagation and are generally perpendicular to the surface normal of a layer of Anderson localization material (e.g., the refractive index variations have filamentary shapes that run from the lower input surface of layer  16  of  FIG.  1    to the upper output surface of layer  16  of  FIG.  1   ). In some configurations, the filaments in an Anderson localization material may be bent, as shown by illustrative structures  16 F near the edge of layer  16  of  FIG.  1   . 
     Anderson localization material can be used to form plates or other optical members such as layer  16  in  FIG.  1   . The plates may be layers with a thickness of at least 0.2 mm, at least 0.5 m, at least 1 mm, at least 2 mm, at least 5 mm, less than 20 mm, or other suitable thickness. Anderson localization material may also be used to form other image transport structures (e.g., straight and/or bent elongated light pipes, spherical shapes, cones, tapered shapes, etc.). As shown in  FIG.  1   , the surfaces of image transport layers such a layer  16  may be planar and/or may have curved profiles (e.g., the edges of device  10  may have rounded outer surfaces). These surfaces may be formed by performing operations such as slicing operations, grinding operations, and polishing operations on blocks of Anderson localization material. 
     Illustrative Anderson localization material for forming layer  16  is shown in  FIG.  10   . As shown in  FIG.  10   , Anderson localization material  72  contains a random (pseudorandom) set of elongated optical structures  74  (e.g., filaments with different refractive index values). The filaments are distributed laterally with a random (pseudorandom) pattern. Material  72  may contain elongated optical structures (e.g., filaments) with  2 - 4 , at least 2, at least 3, at least 4, fewer than 6, fewer than 5, or other suitable number of different materials of different respective refractive index values. 
     To absorb stray light within an image transport layer formed from Anderson localization material, the Anderson localization material may include light absorbing material in low-index filaments.  FIG.  11    is a top view of Anderson localization material with high-index filaments and low-index filaments that include light absorbing material. As shown in  FIG.  11   , Anderson localization material  72  has two (or more) different types of polymer with different refractive index values. The filaments may include, for example, first filaments  76  interspersed with second filaments  78 . First filaments  76  and second filaments  78  may have different respective refractive index values. For example, first filaments  76  may have a lower refractive index than second filaments  78 . Additional filaments having different refractive indices may be used if desired. 
     The locations of filaments  76  and filaments  78  may be randomized laterally within Anderson localization material  72  (e.g., filaments  76  may be located at random locations within the X-Y plane and filaments  78  may be located at the remaining locations within the X-Y plane). The square cross-sectional shapes of each filament in  FIG.  11    is merely illustrative. Each filament may have a cross-section of any desired shape. 
     Each low-index filament  76  in Anderson localization material  72  may include one or more portions of light absorbing material  80 . Light absorbing material  80  may be light absorbing filaments formed from gray or black polymer layer. Alternatively, an absorbing additive (e.g., black dye, black pigment, etc.)  80  may be added to filaments  76 . Incorporating light absorbing material into the low-index filaments in this manner results in stray light that is not guided by high-index filaments  78  being absorbed. 
     Light absorbing materials for the fibers and Anderson localization material of  FIGS.  5 - 11    may be characterized as having a refractive index n and an extinction coefficient k. The extinction coefficient k (sometimes referred to as a k-parameter) of a material may be related to the absorption associated with that material. A lower k-parameter may correspond to higher absorption. The transparent polymers used to form image transport layer  16  may have k-parameters of between 0.01 and 0.1, greater than 0.01, approximately (e.g., within 10% of) 0.05, or any other desired magnitude. The light absorbing material may have a k-parameter of approximately 0.0005, less than 0.001, less than 0.01, between 0.0001 and 0.001 or any other desired magnitude. Said another way, the light absorbing material (e.g., a 100 micron thick piece of the light absorbing material) may absorb (e.g., may have an absorption percentage) between 25% and 75% of incident light, between 40% and 60% of the incident light, more than 5% of the incident light, more than 10% of the incident light, more than 25% of the incident light, more than 50% of the incident light, more than 60% of the incident light, more than 75% of the incident light, more than 80% of the incident light, less than 90% of the incident light, etc. In general, the absorbance of the light absorbing material may be tuned to optimize the performance of the image transport layer and electronic device display. 
     There are many ways to produce image transport layers having light absorbing material of the type shown in  FIGS.  5 - 11   . Fibers for image transport layer  16  may, for example, be extruded using an extruder.  FIG.  12    is a diagram of an illustrative extruder that may be used to manufacture a fiber bundle. As shown in  FIG.  12   , extruder  82  may have hoppers  90  that contain raw material (e.g., polymers) for the different portions of image transport layer. A first hopper  90 - 1  may contain raw material  58 R (e.g., a clear polymer) of a first refractive index for forming binder  58 . A second hopper  90 - 2  may contain raw material  56 R (e.g., a clear polymer) of a second refractive index that is lower than the first refractive index. Raw material  56 R may be used to form fiber cladding  56 . A third hopper  90 - 3  may contain raw material  54 R (e.g., a clear polymer) that is used to form fiber cores  54 . Polymer  54 R may have a third refractive index that is higher than the second refractive index. Raw materials  54 R,  56 R, and  58 R may be pellets for different types of polymers, in one example. 
     To incorporate stray light absorbing material into the fibers, a light absorbing additive  62  may be added to hopper  90 - 1  (in addition to the binder raw material  58 R). In this arrangement, the additive will be distributed throughout binder layer  58  of the fibers  52  produced by extruder  82 . 
     The different polymers in hoppers  90  may be heated to soften and/or liquefy these polymers so that these different polymers may be extruded through extruder die  84  to form fibers such as fibers  52 . Extruder die  84  may include numerous melt distribution plates  86  and a spinneret  88 . Melt distribution plates  86  (sometimes referred to as distribution plates  86 , die plates  86 , etc.) may guide the polymer material through the die to form fibers having desired shapes and dimensions. Spinneret  88  (sometimes referred to as die outlet plate  48 ) may form an outlet for die  84 . The spinneret may have a number of openings. A corresponding fiber or fiber bundle may be output from each opening. There may be any desired number of openings in the spinneret (e.g., more than 100 openings, more than 1,000 openings, more than 5,000 openings, more than 10,000 openings, more than 20,000 openings, between 10,000 and 50,000 openings, between 10,000 and 30,000 openings, more than 100,000 openings, more than 150,000 openings, less than 300,000 openings, between 100,000 and 200,000 openings, between 150,000 and 200,000 openings, etc.). 
     In some cases, as show in  FIG.  3   , one individual fiber  52  may be output from each opening in spinneret  48 . Alternatively, each opening in spinneret  48  may output a respective fiber bundle. Each fiber bundle may have a plurality of fibers  52  distributed in binder material  58 . A process of this type in which fiber bundles each containing a plurality of fibers are extruded from die  84  may be referred to as islands-in-the-sea (IITS) extrusion. Extrusion die  84  may sometimes therefore be referred to as islands-in-the-sea extrusion die  84 . 
     The extrusion process of  FIG.  12    may be used to produce fibers of the type shown in  FIG.  5    (e.g., fibers having a light absorbing additive  62  distributed throughout binder layer  58 ).  FIG.  13    is a diagram of an illustrative extruder that may be used to instead produce fibers of the type shown in  FIG.  6   . As shown in  FIG.  13   , a light absorbing additive  62  may be added to hopper  90 - 2  (in addition to the cladding raw material  56 R). In this arrangement, the additive will be distributed throughout cladding  56  of the fibers  52  produced by extruder  82 . The fibers  52  produced using the extruder of  FIG.  13    therefore may have an arrangement of the type shown in  FIG.  6    (with light absorbing additive evenly distributed throughout cladding  56 ). 
     As shown in  FIGS.  7 - 9   , in some cases light absorbing material may not be evenly distributed throughout another component in fiber  52 . Instead, a separate layer of light absorbing material may be included in each fiber  52  (as in  FIGS.  7  and  8   ) or strips of light absorbing material may be distributed around cladding  56  (as in  FIG.  9   ).  FIG.  14    is a diagram of an illustrative extruder that may be used to produce fibers having separately formed light absorbing layers. 
     As shown in  FIG.  14   , a first hopper  90 - 1  may contain raw material  58 R (e.g., a clear polymer) for forming binder  58 . A second hopper  90 - 2  may contain raw material  56 R (e.g., a clear polymer) for forming cladding  56 . A third hopper  90 - 3  may contain raw material  54 R for forming cores  54 . Additionally, the extruder of  FIG.  14    includes a separate hopper  90 - 4  that contains raw material  64 R for forming a light absorbing layer  64  in fiber  52 . Hopper  90 - 4  may contain a gray or black polymer for forming light absorbing layer  64 . Alternatively, hopper  90 - 4  may contain raw material for a transparent polymer and a light absorbing additive. Ultimately, hopper  90 - 4  may be used to provide material that forms light absorbing layer  64  in  FIG.  7  or  8   . The extruder of  FIG.  14    may produce fibers  52  of the type shown in  FIG.  7    or of the type shown in  FIG.  8   . If two transparent claddings are included in each fiber (as shown in  FIG.  8   ), raw material  56 R in hopper  90 - 2  may optionally provide the raw material for both claddings  56 - 1  and  56 - 2 . Alternatively, a fifth hopper with an additional raw material may be used in cases where claddings  56 - 1  and  56 - 2  are formed from different materials. 
     An extruder of the type shown in  FIG.  14    may also be used to form the fibers of  FIG.  9   . Light absorbing portions  70  in  FIG.  9    may be co-extruded with cores  54  and cladding  56 . The raw material for light absorbing portions  70  may be contained in a dedicated hopper (e.g., hopper  90 - 4  in  FIG.  14   ). 
     The light absorbing layers  64  of  FIGS.  7  and  8    may also be formed on fibers  52  after the fibers are extruded. After extrusion, melt-spinning may solidify the fibers. The fibers may be produced having core  54  and cladding  56  (e.g., without light absorbing layer  64 ). Once solidified, a light absorbing coating may be applied to cladding  56  to form light absorbing layer  64 . The light absorbing coating may be a curable coating (e.g., an ultraviolet-light-curable coating) that is cured after being applied to the fibers. 
     In the examples of  FIGS.  12 - 14   , extruder  82  is used to extrude fibers  52  or fiber bundles that include numerous fibers  52 . This example is merely illustrative. An extruder may instead be used to extrude a preform that is subsequently drawn to form one or more fibers in a draw tower. Elongated cylindrical polymer preforms and polymer preforms of other shapes may be formed into elongated strands (e.g., fibers). Equipment such as a draw tower or other equipment for forming elongated polymer into strands may be used. As part of the drawing process, the lateral dimensions of the drawn material will shrink, so this type of process may help ensure that optical structures have desired lateral dimensions. 
     An illustrative draw tower is shown in  FIG.  15   . As shown in  FIG.  15   , draw tower  102  may have an adjustable feeder  92  such as a feeder based on a computer-controlled screw feed. Feeder  92  may be adjusted to adjust the speed at which preform  94  is lowered between heated walls  96  and  98 . Walls  96  and  98  may surround preform  94  radially (e.g., walls  96  and  98  may be cylindrical and preform  94  may, during drawing operations, be lowered into the center of the cylindrical cavity formed by the cylindrical walls). The cylindrical walls may be heated to form an oven that heats preform  94 . For example, walls  96  may be heated to a first (preheating) temperature and walls  98  may be heated to a second (hot zone) temperature. The first temperature may be sufficiently high to help preheat preform  94  (e.g., 130° C.) and the second temperature may be a higher working temperature (e.g., 180-200° C.) that causes preform  94  to soften and thereby form neck  100 . This allows the polymer material of preform  94  to be drawn out of drawing tower  102  in direction  106  as thin fiber  104 . If desired, the draw temperature (working temperature) used in draw tower  102  may be above the melting temperature of the materials being drawn. 
       FIGS.  16  and  17    show examples of preforms  100  that may be drawn to form fibers having desired arrangements. Preforms  100  may include coextruded polymer (e.g., formed using an extruder of the type shown in  FIGS.  12 - 14   ). Alternatively, some or all of the preform may be formed by polymer raw material (e.g., polymer pellets). 
     As shown in  FIG.  16   , preform  100  may include raw material  54 R for forming core  54  of fiber  52 . Raw material  54 R may be contained within a cladding portion such as cladding portion  112 . Cladding portions  112  and  114  may be formed by tubes of a transparent polymer and may serve to improve the speed and ease of manufacturing fibers. Raw material  56 R for forming cladding portion  116  may be formed between cladding portions  112  and  114 . 
     After preform  100  is drawn (e.g., using the draw tower of  FIG.  15   ) into a fiber, the resulting fiber may have a cladding  56  that includes three portions (formed by cladding portion  112 , cladding portion  116 , and cladding portion  114 ). The cladding portions  112  and  114  may be sufficiently thin so that cladding portion  116  comprises the majority of the cladding in the final fiber. Cladding portions  112  and  114  may be formed from the same material as cladding material  56 R or may be formed from a different material than cladding material  56 R. In one example, cladding portions  112  and  114  may be formed from poly(methyl methacrylate) (PMMA) and raw material  56 R may be a fluoropolymer such as THV (terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride). These examples are merely illustrative and in general each component in preform  100  may be formed from any desired material. 
     In  FIG.  16   , light absorbing material  70  may be formed in cladding portion  116  alongside raw material  56 R. As shown, the light absorbing material  70  may be formed in cladding portion  116  at the interface between cladding portions  116  and  114 . Forming the light absorbing material at the outer part of cladding portion  116  ensures that light guided by core  54  in the fiber is less likely to be exposed to the light absorbing material. Light absorbing material  70  may be formed by a pre-drawn light absorbing fiber. Light absorbing fibers  70  may optionally be formed from the same or a similar material as raw material  56 R for minimal disruption to the preform drawing conditions. For example, if raw material  56 R is transparent THV, light absorbing fibers  70  may be formed from black THV. 
     After preform  100  of  FIG.  16    is drawn, the resulting fiber  52  may have an arrangement similar to as shown in  FIG.  9   . The light absorbing material is formed at an outer part of cladding  56 . Any desired number of light absorbing fibers  70  may be incorporated into the preform (e.g., four, eight, more than eight, more than twenty, more than fifty, more than one hundred, less than one hundred, less than ten, less than five, etc.). 
       FIG.  17    shows another example of a preform with light absorbing material  70 . In  FIG.  17   , light absorbing material  70  is incorporated into cladding portion  114 . Cladding portion  114  may be co-extruded with light absorbing material  70  such that the tube has localized regions (lines) of black light absorbing material. Light absorbing material  70  may be formed from the same polymer as cladding portion  114 . For example, light absorbing material  70  may be formed by black PMMA that is co-extruded with transparent PMMA that forms the rest of cladding portion  114 . 
     In yet another embodiment, light absorbing material may be uniformly distributed throughout cladding portion  114 . In other words, a uniformly gray or black PMMA cladding portion  114  may be used to form the light absorbing portion of the preform. 
     Additionally, instead of co-extruding light absorbing portions  70  with cladding portion  114 , pre-drawn light absorbing fibers  70  may be heat-melted onto the outer surface of cladding portion  114  during preform assembly. In other words, the light absorbing fibers  70  may be heated while applied to the outer surface of cladding portion  114 . As cladding portion  114  and light absorbing fibers  70  soften (and/or liquefy), the light absorbing fibers may become integrated with cladding portion  114 . The cladding portion may then be allowed to cool, securing the light absorbing fibers  70  at the outer surface of the cladding portion. Cladding portion  114  may be formed from transparent PMMA and light absorbing fibers  70  may be formed from black PMMA, black polyvinylidene fluoride (PVDF), or another desired material. 
     After preform  100  of  FIG.  17    is drawn, the resulting fiber  52  may have an arrangement similar to as shown in  FIG.  9   . The light absorbing material is formed at an outer part of cladding  56 . Any desired number of light absorbing fibers  70  may be incorporated into the preform (e.g., four, eight, more than eight, more than twenty, more than fifty, more than one hundred, less than one hundred, less than ten, less than five, etc.). 
       FIG.  18    is a top view of a fiber  52  formed by drawing preform  100  of  FIG.  16   . As shown, cladding  56  surrounds core  54  and includes portions  112 ,  114 , and  116 . Light absorbing material  70  is formed in cladding portion  116  on the side of cladding portion  116  adjacent to cladding portion  114 .  FIG.  19    is a top view of a fiber  52  formed by drawing preform  100  of  FIG.  17   . As shown, cladding  56  surrounds core  54  and includes portions  112 ,  114 , and  116 . Light absorbing material  70  is formed in cladding portion  114 . After fibers  52  (e.g., from  FIGS.  18  and  19   ) are drawn, the fibers may be fused together to form a coherent fiber bundle that is then used to form image transport layer  16 . 
     To form Anderson localization material with light absorbing material (as shown in  FIG.  11   ), an extruder may be used to extrude elongated members each having areas of transversely randomized refractive index. Light absorbing material may be co-extruded with the elongated low-index members or may be incorporated into the low-index polymer as an additive. After extrusion, a fuser may be used to fuse together the elongated members to form a preform. Then, the preform may be drawn to form fiber. Lengths of the fiber may be fused together to form a material for the image transport layer. 
       FIG.  20    is a flowchart of illustrative steps involved in forming an image transport layer for an electronic device display in accordance with an embodiment. As shown, at step  132 , a preform (such as the preform of  FIG.  16    or  FIG.  17   ) may be assembled. The preform may be at least partially assembled using extrusion. Raw materials (e.g., polymer pellets) may be incorporated into preform. Light absorbing material may also be incorporated into the preform. Next, at step  134 , the preform may be drawn down to form fiber (e.g., using the drawing equipment of  FIG.  15   ). The fiber may then be fused together at step  136  with other fibers having similar or the same structure. This forms a coherent fiber bundle that may undergo additional cutting, shaping, polishing, etc. to form a finished image transport layer. In cases where the fibers are extruded (and not drawn), the extruded fibers may be fused together after extrusion similar to as in step  136  of  FIG.  20   . 
       FIG.  21    is a graph of the amount of light absorbing material in each fiber as a function of position across the image transport layer. In one embodiment, the fibers of image transport layer  16  in device  10  may have a uniform structure across the image transport layer. In other words, the fibers may have the same amount of light absorbing material regardless of the position of the fiber. Profile  120  depicts an arrangement of this type, with the amount of light absorbing material remaining constant across the entire image transport layer. 
     In other arrangements, the amount of light absorbing material in each fiber may vary as a function of position across the image transport layer. The optimal amount of light absorbing material may be higher for the bent fibers at the edge of the image transport layer than in the unbent fibers in the center of the image transport layers. Profiles  122  and  124  show examples where the amount of light absorbing material varies as a function of position. As shown, the amount of light absorbing material may be higher at the edge of the image transport layer than in the center of the image transport layer. There may be a step-change in the amount of light absorbing material (as in profile  122 ) or the amount of light absorbing material may change gradually (as in profile  124 ). The amount of light absorbing material may change in linear, non-linear, or step-wise fashion. 
     It should be understood that the amount of light absorbing material varying as a function of position is merely illustrative. Instead, the absorbance of the light absorbing material may vary as a function of position to achieve the same effect. 
       FIGS.  22 A,  23 A, and  24 A  show additional examples of preforms  100  that may be drawn to form fibers having desired arrangements. Preforms  100  may include coextruded polymer (e.g., formed using an extruder of the type shown in  FIGS.  12 - 14   ). Alternatively, some or all of the preform may be formed by polymer raw material (e.g., polymer pellets). 
     As shown in  FIG.  22 A , preform  100  may include raw material  54 R for forming core  54  of fiber  52 . Raw material  54 R may be contained within a cladding portion such as cladding portion  112 . Cladding portions  112  and  114  may be formed by tubes of a transparent polymer and may serve to improve the speed and ease of manufacturing fibers. Raw material  56 R for forming cladding portion  116  may be formed between cladding portions  112  and  114 . 
     In  FIG.  22 A , protected light absorbing fibers  126  (sometimes referred to as light absorbing filaments, light absorbing fibers, protected light absorbing filaments, sheathed light absorbing filaments, sheathed light absorbing fibers, etc.) are included between cladding portions  112  and  114  in addition to raw material  56 R. The protected light absorbing fibers  126  include a light absorbing core  128  that is formed from a light absorbing material. The protected light absorbing fibers also include a protective sheath  130  for containing the light absorbing material of core  128 . Protective sheath  130  may be transparent and may be referred to as a cladding, protective layer, protective sheath, protective tube, etc. Without protective sheath  130  (e.g., in an arrangement similar to as in  FIG.  16    or  FIG.  17   ), the light absorbing material of core  128  may undesirably diffuse out of the cladding (e.g., into the core or binder). By including protective sheath  130  around each light absorbing core  128 , the light absorbing material is kept in a desired location in the fiber (within the cladding) during subsequent processing. 
     The protected light absorbing fibers  126  may be formed by a pre-drawn light absorbing fiber or may be co-extruded with one or more other components of the preform. Light absorbing cores  128  may optionally be formed from the same or a similar material as raw material  56 R for minimal disruption to the preform drawing conditions. For example, if raw material  56 R is transparent THV, light absorbing cores  128  may be formed from black THV. 
     After preform  100  is drawn (e.g., using the draw tower of  FIG.  15   ) into a fiber, the resulting fiber may have a cladding  56  that includes three portions (formed by cladding portion  112 , cladding portion  116 , and cladding portion  114 ). The cladding portions  112  and  114  may be sufficiently thin so that cladding portion  116  comprises the majority of the cladding in the final fiber. 
     Cladding portions  112  and  114 , cladding material  56 R, and sheaths  130  of the protected light absorbing fibers  126  may be formed from the same material or one or more different materials. Cladding portions  112  and  114 , cladding material  56 R, and sheaths  130  of the protected light absorbing fibers  126  may all be transparent. Cladding portions  112  and  114 , cladding material  56 R, and sheaths  130  of the protected light absorbing fibers  126  may each be formed from a material such as poly(methyl methacrylate) (PMMA), a fluoropolymer such as THV (terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride), polyvinylidene fluoride (PVDF), or EFEP (a terpolymer of ethyelene, tetrafluoroethylene, and hexafluoropropylene), polycarbonate (PC), polystyrene (PS), etc. Light absorbing cores  126  may be formed from black THV or any other desired light absorbing material. In one arrangement, sheaths  130  are formed from a different material than cladding portions  112  and  114 . In one arrangement, sheaths  130  are formed from a different material than raw material  56 R (e.g., the remaining portion of cladding portion  116 ). These examples are merely illustrative and in general each component in preform  100  may be formed from any desired material. 
       FIG.  22 B  is a top view of a fiber  52  formed by drawing preform  100  of  FIG.  22 A . As shown, cladding  56  surrounds core  54  and includes portions  112 ,  114 , and  116 . Sheathed light absorbing fibers  126  (with light absorbing cores  128  and protective sheaths  130 ) are formed in cladding portion  116  (e.g., on the side of cladding portion  116  adjacent to cladding portion  114 ). 
       FIG.  22 A  shows one option for preventing diffusion of light absorbing material out of the cladding (e.g., by encasing the light absorbing fibers in individual transparent protective sheaths). Another option is to include an additional transparent cladding layer (e.g., that is concentric with cladding portions  112  and  114 ). An embodiment of this type is shown in  FIG.  23 A . 
     As shown in  FIG.  23 A , preform  100  may include raw material  54 R for forming core  54  of fiber  52 . Similar to as in  FIG.  22 A , raw material  54 R in  FIG.  23 A  may be contained within a cladding portion such as cladding portion  112 . Cladding portions  112  and  114  may be formed by tubes of a transparent polymer and may serve to improve the speed and ease of manufacturing fibers. Raw material  56 R for forming cladding portion  116  may be formed between cladding portions  112  and  114 . 
     The preform  100  in  FIG.  23 A  also includes an additional cladding portion  138  formed around cladding portion  114  (e.g., cladding portion  114  is interposed between cladding portions  112  and  138 ). The cladding portions  138 ,  112 , and  114  are concentric transparent polymer tubes. 
     In  FIG.  23 A , light absorbing fibers  140  (sometimes referred to as light absorbing filaments) are included between cladding portions  114  and  138 . Positioning the light absorbing fibers between the cladding portions  114  and  138  may prevent the light absorbing fibers from diffusing into the fiber core or binder layer. 
     The light absorbing fibers  140  may be formed by a pre-drawn light absorbing fiber or may be co-extruded with one or more other components of the preform. Light absorbing fibers  140  may optionally be formed from the same or a similar material as raw material  56 R for minimal disruption to the preform drawing conditions. For example, if raw material  56 R is transparent THV, light absorbing fibers  140  may be formed from black THV. 
     Similar to as discussed in connection with  FIG.  22 A , cladding portions  112 ,  114 , and  138  as well as cladding material  56 R may all be formed from the same material or one or more different materials (e.g., PMMA, THV, PVDF, EFEP, PC, PS, etc.). Cladding portions  112 ,  114 , and  138  as well as cladding material  56 R may all be transparent. Light absorbing fibers  140  may be formed from black THV or any other desired light absorbing material. These examples are merely illustrative and in general each component in preform  100  may be formed from any desired material. 
       FIG.  23 B  is a top view of a fiber  52  formed by drawing preform  100  of  FIG.  23 A . As shown, cladding  56  surrounds core  54  and includes portions  112 ,  114 ,  116 , and  138 . Cladding  56  also includes light absorbing fibers  140  between cladding portions  114  and  138 . 
       FIG.  24 A  shows a preform having a similar arrangement to the preform of  FIG.  23 A . Specifically, preform  100  of  FIG.  24 A  includes raw material  54 R contained within a cladding portion  112 . Raw material  56 R for forming cladding portion  116  may be formed between cladding portions  112  and  114 . The preform also includes an additional cladding portion  138  formed around cladding portion  114  (e.g., cladding portion  114  is interposed between cladding portions  112  and  138 ). The cladding portions  138 ,  112 , and  114  are concentric transparent polymer tubes. 
     However, instead of incorporating light absorbing fibers  140  between cladding portions  114  and  138  (e.g., light absorbing islands as in  FIG.  23 A ), the preform of  FIG.  24 A  includes a light absorbing ring  142  between cladding portions  114  and  138 . The light absorbing ring  142  may be co-extruded with one or more other components of the preform (e.g., may be co-extruded with adjacent cladding portions  114  and  138 ), may be applied as a coating on cladding portion  114 , may be formed using pellets, etc. Ultimately, the light absorbing material  142  forms a ring around the core (e.g., concentric with cladding portions  112 ,  114 ,  116 , and  138 . Light absorbing ring  142  (sometimes referred to as light absorbing tube  142 ) may be formed from black THV or any other desired light absorbing material. In general, each component in preform  100  may be formed from any desired material. 
       FIG.  24 B  is a top view of a fiber  52  formed by drawing preform  100  of  FIG.  24 A . As shown, cladding  56  surrounds core  54  and includes transparent portions  112 ,  114 ,  116 , and  138 . Cladding  56  also includes light absorbing material  142  (e.g., a light absorbing tube) between cladding portions  114  and  138 . 
     The drawing and fusing process of  FIG.  21    may be used to form a coherent fiber bundle using any of the preforms of  FIGS.  22 A,  23 A, and  24 A . 
       FIGS.  25 A and  25 B  show another possible technique for forming light absorbing material in a fiber cladding.  FIG.  25 A  shows a top view of a fiber with a core and cladding in a binder material. As shown, fiber  52  includes a core  54  and cladding  56  and is surrounded by binder material  58 . However, in  FIG.  25 A , a light absorbing material  144  is distributed throughout binder  58 . 
     The light absorbing material  144  may be black pigment, black dye, or other light absorbing material that absorbs and blocks light (e.g., carbon black based material, carbon nanotubes, graphite nanoplatelets, etc.). Additionally, the light absorbing material  144  may be doped to cause a preferential attraction to the material of cladding  56 . For example, in the scenario in which cladding  56  is formed from a fluoropolymer such as THV, light absorbing material  144  may be fluorine-doped. 
     Upon the application of heat to the fiber  52  and binder material  58 , the doped light absorbing material preferentially aggregates on the surface of cladding  56 .  FIG.  25 B  is a top view of the fiber after heat has been applied. As shown, the doped light absorbing material  144  aggregates on an outer surface  146  of cladding  56 . The light absorbing material  144  may be considered a part of cladding  56  (e.g., cladding  56  has a transparent portion with an outer surface and a light absorbing coating on the outer surface of the transparent portion). 
     In one illustrative example, the transparent portion of cladding  56  may be formed form a fluoropolymer such as THV, PVDF, or EFEP. The light absorbing material may therefore be fluorine-doped, resulting in a preferential attraction between the light absorbing material and transparent cladding material. Light absorbing material  144  may be a fluorine-doped black dye, as one example. 
     It should be noted that the illustrative fiber (with a core  54  and transparent cladding portion  56 ) depicted in  FIGS.  25 A and  25 B  is merely illustrative. If desired, the cladding may have one or more layers (e.g., as shown in connection with  FIG.  7   ,  FIG.  8   ,  FIG.  18   ,  FIG.  19   , etc). The technique of  FIGS.  25 A and  25 B  may be used as long as the outer-most transparent cladding layer and the doped light absorbing additive have a preferential attraction to one another (resulting in the light absorbing additives aggregating on the outer surface of the cladding). One or more additional interior cladding layers (of any desired material) may optionally be included in the fiber without disrupting the desired final arrangement (of having light absorbing material on an outer surface of the cladding). 
       FIG.  26    is a flowchart of illustrative steps involved in forming fibers with a light absorbing coating on an outer surface of the cladding in accordance with an embodiment. At step  148 , the doped light absorbing material (e.g., fluorine-doped black dye) may be distributed throughout the binder material. The binder material (e.g., the host binder material in which the dye is mixed) may be transparent. The light absorbing material may be mixed with the transparent binder raw material during extrusion, in one example. Twin screw extrusion (TSE), single screw extrusion (SSE), or brabender extrusion may be used for combining the transparent binder raw material and doped light absorbing dye. In general, any desired manufacturing techniques may be used to form the fibers surrounded by a binder material having a distributed doped light absorbing dye. The fibers may undergo melt-spinning or other processing during manufacturing. 
     Next, at step  150 , heat may be applied to cause the doped light absorbing material to preferentially aggregate on the cladding surface. Heat may be applied at one or more times during the formation of the fibers and coherent fiber bundles. Heat may be applied as multiple fibers are fused together to form a coherent fiber bundle, during annealing of the coherent fiber bundle, etc. These applications of heat cause the doped light absorbing material that is mixed in the binder material to aggregate on the outer surface of the fiber cladding (e.g., as shown in  FIG.  25 B ). 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20200615
Publication Date: 20231003
Grant Date: 20231003
Priority Date: 20190829
Inventors: GUILLOU, Jean-Pierre S.
BROWN, MICHAEL J.
WITTENBERG, MICHAEL B.
LIN, WEI
KARBASI, SALMAN
MAJUMDAR, SHUBHADITYA
CLARK, IAN T.
GUPTA, NATHAN K.
GULGUNJE, Prabhakar
HUANG, CHUNCHIA
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B5/003", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B1/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0063", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0017", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/003", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B1/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K5/0017", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0063", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0063", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B1/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/003", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/06", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 88195999