WO2024129205A1 - High transmission large area metalenses - Google Patents

Abstract

A metalens and a light source including the metalens are disclosed, the metalens having an area of over 1 mm and a metasurface configured to increase transmission by avoiding Mie resonances at wavelengths of light received by the metalens.

Description

HIGH TRANSMISSION LARGE AREA METALENSES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit of priority to U.S. Provisional Patent Application No. 63/432,944 titled “HIGH TRANSMISSION LARGE AREA METALENSES” and filed December 15, 2022, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates generally to metalenses and their use in LEDs, pcLEDs, LED and pcLED arrays, and applications including LEDs, pcLED, LED and pcLED arrays including a metalens.

BACKGROUND

[0003] Semiconductor light emitting diodes and laser diodes (collectively referred to herein as “LEDs”) are among the most efficient light sources currently available. The emission spectrum of an LED typically exhibits a single narrow peak at a wavelength determined by the structure of the device and by the composition of the semiconductor materials from which it is constructed. By suitable choice of device structure and material system, LEDs may be designed to operate at ultraviolet, visible, or infrared wavelengths.

[0004] LEDs may be combined with one or more wavelength converting materials (generally referred to herein as “phosphors”) that absorb light emitted by the LED and in response emit light of a longer wavelength. For such phosphor-converted LEDs (“pcLEDs”), the fraction of the light emitted by the LED that is absorbed by the phosphors depends on the amount of phosphor material in the optical path of the light emitted by the LED, for example on the concentration of phosphor material in a phosphor layer disposed on or around the LED and the thickness of the layer. Phosphor-converted LEDs may be designed so that all the light emitted by the LED is absorbed by one or more phosphors, in which case the emission from the pcLED is entirely from the phosphors. In such cases the phosphor may be selected, for example, to emit light in a narrow spectral region that is not efficiently generated directly by an LED.

Alternatively, pcLEDs may be designed so that only a portion of the light emitted by the LED is absorbed by the phosphors, in which case the emission from the pcLED is a mixture of light emitted by the LED and light emitted by the phosphors. By suitable choice of LED, phosphors, and phosphor composition, such a pcLED may be designed to emit, for example, white light having a desired color temperature and desired color-rendering properties.

[0005] Inorganic LEDs and pcLEDs have been widely used to create different types of displays, matrices and light engines including automotive adaptive headlights, augmented-reality (AR) displays, virtual -reality (VR) displays, mixed-reality (MR) displays (AR, VR, and MR systems referred to herein as visualization systems), smart glasses and displays for mobile phones, smart watches, monitors and TVs, and flash illumination for cameras in mobile phones. Individual LEDs or pcLEDs in these architectures can have an area of a few square millimeters down to a few square micrometers (e.g., microLEDs) depending on the matrix or display sized and its pixel per inch requirements.

SUMMARY

[0006] This specification discloses lighting devices, the lighting devices including a light source configured to emit light having wavelengths within a wavelength range; and a metalens positioned to receive the light, the metalens including a metasurface disposed on a substrate, the metasurface configured to affect a phase of the light received by the metalens from the light source to produce an optical effect in the light and configured not to exhibit Mie resonances within the wavelength range of the light. The metasurface may include an array of meta-atoms, the meta-atoms extending radially around an optical axis of the metalens, the meta-atoms spaced apart at a pitch, the pitch having a value less than a shortest wavelength in the wavelength range, the meta-atoms arranged and varying in size to affect a phase change of light without the metasurface exhibiting Mie resonances. The meta-atoms may be pillars having a height and a diameter, the height of the pillars may be a constant value over the metasurface, and a value of the pitch may be set so the diameter of the pillars is varied radially between adjacent pillars to affect the phase change of the light without the metasurface exhibiting Mie resonances. The height of the pillars may be less than 280 nm. The height of the pillars may be between 220 nm and 260 nm. The wavelength range may be in the visible light range and the optical effect may be to collimate the light, the pitch may be less than 240 nm, and the diameter of the pillars may be varied to affect a phase change between 0 and 2 in the light. The diameter of the pillars may vary between 40 nm and 170 nm. The metalens may have a diameter on a side facing the light source of 1 mm or more. The diameter may be 5 mm and the optical effect may be collimating the light.

[0007] In another aspect, a metalens is disclosed, the metalens including a substrate and a metasurface disposed directly on the substrate, the metasurface including a dielectric material and having a structure, the structure including an array of pillars extending radially from an optical axis of the metasurface, the pillars having a height that is a fixed value and a diameter that varies, and the pillars spaced apart at a pitch of 240 nm or less. The diameter of the pillars may vary to affect a phase change between 0 and 2u in light between the wavelengths of 400 nm and 700 nm. The diameter of the pillars may be less than 170 nm. The pitch may be 220 nm and the diameter of the pillars may vary between 40 nm and 170 nm.

[0008] The light sources and metalenses disclosed herein may be used for example in the various devices and applications listed above in the Background section.

[0009] These and other embodiments, features and advantages of the present invention will become more apparent to those skilled in the art when taken with reference to the following more detailed description of the invention in conjunction with the accompanying drawings that are first briefly described

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows a schematic cross-sectional view of an example pcLED.

[0011] FIGs. 2A and 2B show, respectively, cross-sectional and top schematic views of an array of pcLEDs. FIG. 2C shows a schematic top view of an LED wafer from which LED arrays such as those illustrated in FIGs. 2A and 2B may be formed.

[0012] FIG. 3 A shows a schematic top view of an electronics board on which an array of LEDs or pcLEDs may be mounted, and FIG. 3B similarly shows an array of pcLEDs mounted on the electronic board of FIG. 3 A.

[0013] FIG. 4A shows a schematic cross-sectional view of an array of pcLEDs arranged with respect to waveguides and a projection lens. FIG. 4B shows an arrangement similar to that of FIG. 4A, without the waveguides.

[0014] FIG. 5 schematically illustrates an example camera flash system.

[0015] FIG. 6 schematically illustrates an example display system.

[0016] FIG. 7 shows a block diagram of an example visualization system.

[0017] FIG. 8 is a cross-sectional view of a lighting device 800 having a metalens. [0018] FIG. 9A is a perspective view of a portion of example metalens. FIG. 9B is a cross- sectional view of a segment of the metalens shown in FIG. 9A. FIG. 9C is a cross-sectional view of a segment of a metalens having pillars with constant heights.

[0019] FIG. 10 a graph of measured transmission of four sample metalenses across the visible wavelength range from 400 nm to 800 nm.

[0020] FIG. 11 A is a graph of simulated transmission for 4 different metasurfaces at a wavelength of 450 nm for a range of pillar diameters. FIG. 1 IB is a graph of the relative phase of light as a function of pillar diameter D at 450 nm for metasurfaces with the same parameters as shown in FIG. HA.

[0021] FIG. 12 is a graph of simulated transmission data for an example metalens in which the height H of the pillars is held constant and 800 nm and the pitch (period) P is reduced to 220 nm at three wavelengths 450 nm, 532 nm, and 650 nm.

[0022] FIG. 13 is a plot of simulated transmission and refection data across the visible wavelength range from 400 to 750 nm for a metalens with a metasurface structure that avoids Mie resonances.

[0023] FIG. 14A is a plan view of a metalens having a metasurface structure that avoids Mie resonances. FIG. 14B is an expansion of region 14B marked in FIG. 14A. FIG. 14C is an expansion of region 14C marked in FIG. 14A.

[0024] FIG. 15 illustrates determination of pillar diameters as a function of position in the metalens for a phase variation of 0 to 2TT.

DETAILED DESCRIPTION

[0025] The following detailed description should be read with reference to the drawings, in which identical reference numbers refer to like elements throughout the different figures. The drawings, which are not necessarily to scale, depict selective embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention.

[0026] FIG. 1 shows an example of an individual pcLED 100 comprising a light emitting semiconductor diode (LED) structure 102 disposed on a substrate 104, and a phosphor layer 106 (which may also be referred to herein as a wavelength converting structure) disposed on the LED. Light emitting semiconductor diode structure 102 typically comprises an active region disposed between n-type and p-type layers. Application of a suitable forward bias across the diode structure results in emission of light from the active region. The wavelength of the emitted light is determined by the composition and structure of the active region.

[0027] The LED may be, for example, a III-Nitride LED that emits ultraviolet, blue, green, or red light. LEDs formed from any other suitable material system and that emit any other suitable wavelength of light may also be used. Other suitable material systems may include, for example, III-Phosphide materials, III-Arsenide materials, and II- VI materials.

[0028] Any suitable phosphor materials may be used, depending on the desired optical output and color specifications from the pcLED. Phosphor layers may for example comprise phosphor particles dispersed in or bound to each other with a binder material or be or comprise a sintered ceramic phosphor plate.

[0029] FIGs. 2A-2B show, respectively, cross-sectional and top views of an array 200 of pcLEDs 100 including phosphor layers 106 disposed on a substrate 202. Such an array may include any suitable number of pcLEDs arranged in any suitable manner. In the illustrated example the array is depicted as formed monolithically on a shared substrate, but alternatively an array of LEDs or pcLEDs may be formed from individual mechanically separate LEDs or pcLEDs. Substrate 202 may optionally comprise CMOS circuitry for driving the LEDs and may be formed from any suitable materials.

[0030] Although FIGs. 2A-2B show a three-by-three array of nine pcLEDs, such arrays may include for example tens, hundreds, or thousands of LEDs or pcLEDs. Individual LEDs or pcLEDs may have widths (e.g., side lengths) in the plane of the array of, for example, less than or equal to 1 millimeter (mm), less than or equal to 500 microns, less than or equal to 100 microns, less than or equal to 50 microns, or less than or equal to 10 microns. LEDs in such an array may be spaced apart from each other by streets or lanes having a width in the plane of the array of, for example, hundreds of microns, less than or equal to 100 microns, less than or equal to 50 microns, less than or equal to 10 microns, or less than or equal to 5 microns. Although the illustrated examples show rectangular LEDs or pcLEDs arranged in a symmetric matrix, the LEDs or pcLEDs and the array may have any suitable shape or arrangement and need not all be of the same shape or size. For example, LEDs or pcLEDs located in central portions of an array may be larger than those located in peripheral portions of the array. Alternatively, LEDs or pcLEDs located in central portions of an array may be smaller than those located in peripheral portions of the array.

[0031] FIG. 2C shows a schematic top view of a portion of an LED wafer 210 from which LED arrays such as those illustrated in FIGS. 2A and 2B may be formed. FIG. 2C also shows an enlarged 3x3 portion of the wafer. In the example wafer individual LEDs or pcLEDs 111 having side lengths (e.g., widths) of Wi are arranged as a square matrix with neighboring LEDs or pcLEDs having a center-to-center distances Di and separated by lanes 113 having a width W2. Wi may be, for example, less than or equal to 1 millimeter (mm), less than or equal to 500 microns, less than or equal to 100 microns, less than or equal to 50 microns, or less than or equal to 10 microns. W2 may be, for example, hundreds of microns, less than or equal to 100 microns, less than or equal to 50 microns, less than or equal to 10 microns, or less than or equal to 5 microns. Di = Wi + W2. WI may also be, for example, greater than 1 mm, for example, between 2 mm and 5 mm, for instance 2.4 mm, or larger.

[0032] An array may be formed, for example, by dicing wafer 210 into individual LEDs or pcLEDs and arranging the dice on a substrate. Alternatively, an array may be formed from the entire wafer 210, or by dividing wafer 210 into smaller arrays of LEDs or pcLEDs.

[0033] LEDs or pcLEDs having dimensions in the plane of the array (e.g., side lengths) of less than or equal to about 50 microns are typically referred to as microLEDs, and an array of such microLEDs may be referred to as a microLED array.

[0034] In an array of pcLEDs, all pcLEDs may be configured to emit essentially the same spectrum of light. Alternatively, a pcLED array may be a multicolor array in which different pcLEDs in the array may be configured to emit different spectrums (colors) of light by employing different phosphor compositions. Similarly, in an array of direct emitting LEDs (i.e., not wavelength converted by phosphors) all LEDs in the array may be configured to emit essentially the same spectrum of light, or the array may be a multicolor array comprising LEDs configured to emit different colors of light.

[0035] The individual LEDs or pcLEDs in an array may be individually operable (addressable) and/or may be operable as part of a group or subset of (e.g., adjacent) LEDs or pcLEDs in the array.

[0036] An array of LEDs or pcLEDs, or portions of such an array, may be formed as a segmented monolithic structure in which individual LEDs or pcLEDs are electrically isolated or partially electrically isolated from each other by trenches and/or insulating material, but the electrically isolated or partially electrically isolated segments remain physically connected to each other by other portions of the semiconductor structure. For example, in such a monolithic structure the active region and a first semiconductor layer of a first conductivity type (n or p) on one side of the active region may be segmented, and a second unsegmented semiconductor layer of the opposite conductivity type (p or n) positioned on the opposite side of the active region from the first semiconductor layer. The second semiconductor layer may then physically and electrically connect the segmented structures to each other on one side of the active region, with the segmented structures otherwise electrically isolated from each other and thus separately operable as individual LEDs.

[0037] An LED or pcLED array may therefore be or comprise a monolithic multicolor matrix of individually operable LED or pcLED light emitters. The LEDs or pcLEDs in the monolithic array may for example be microLEDs as described above.

[0038] A single individually operable LED or pcLED or a group of adjacent such LEDs or pcLEDs may correspond to a single pixel (picture element) in a display. For example, a group of three individually operable adjacent LEDs or pcLEDs comprising a red emitter, a blue emitter, and a green emitter may correspond to a single color-tunable pixel in a display.

[0039] As shown in FIGs. 3A-3B, an LED or pcLED array 200 may for example be mounted on an electronics board 300 comprising a power and control module 302, a sensor module 304, and an attach region 306. Power and control module 302 may receive power and control signals from external sources and signals from sensor module 304, based on which power and control module 302 controls operation of the LEDs/pcLEDs. Sensor module 304 may receive signals from any suitable sensors, for example from temperature or light sensors. Alternatively, array 200 may be mounted on a separate board (not shown) from the power and control module and the sensor module.

[0040] Individual LEDs or pcLEDs may optionally incorporate or be arranged in combination with a lens or other optical element located adjacent to or disposed on the LED or the phosphor layer of the pcLED. Such an optical element, not shown in the figures, may be referred to as a “primary optical element”. In addition, as shown in FIGs. 4A-4B an array 200 (for example, mounted on an electronics board 300) may be arranged in combination with secondary optical elements such as waveguides, lenses, or both for use in an intended application. In FIG. 4A, light emitted by pcLEDs 100 is collected by waveguides 402 and directed to projection lens 404. Projection lens 404 may be a Fresnel lens, for example. This arrangement may be suitable for use, for example, in automobile headlights. In FIG. 4B, light emitted by pcLEDs 100 is collected directly by projection lens 404 without use of intervening waveguides. This arrangement may be particularly suitable when LEDs or pcLEDs can be spaced sufficiently close to each other and may also be used in automobile headlights as well as in camera flash applications. A microLED display application may use similar optical arrangements to those depicted in FIGs. 4A-4B, for example.

[0041] In another example arrangement, a central block of LEDs or pcLEDs in an array may be associated with a single common (shared) optic, and edge LEDs or pcLEDs located in the array at the periphery of the central bloc are each associated with a corresponding individual optic.

[0042] Generally, any suitable arrangement of optical elements may be used in combination with the LED and pcLED arrays described herein, depending on the desired application.

[0043] LED and pcLED arrays as described herein may be useful for applications requiring or benefiting from fine-grained intensity, spatial, and temporal control of light distributions. These applications may include, but are not limited to, precise special patterning of emitted light from individual LEDs or pcLEDs or from groups (e g., blocks) of LEDs or pcLEDs. Depending on the application, emitted light may be spectrally distinct, adaptive over time, and/or environmentally responsive. Such arrays may provide pre-programmed light distribution in various intensity, spatial, or temporal patterns. The emitted light may be based at least in part on received sensor data and may be used for optical wireless communications. Associated electronics and optics may be distinct at an individual LED / pcLED, group, or device level.

[0044] An array of independently operable LEDs or pcLEDs may be used in combination with a lens, lens system, or other optic or optical system (e.g., as described above) to provide illumination that is adaptable for a particular purpose. For example, in operation such an adaptive lighting system may provide illumination that varies by color and/or intensity across an illuminated scene or object and/or is aimed in a desired direction. Beam focus or steering of light emitted by the LED or pcLED array can be performed electronically by activating LEDs or pcLEDs in groups of varying size or in sequence, to permit dynamic adjustment of the beam shape and/or direction without moving optics or changing the focus of the lens in the lighting apparatus. A controller can be configured to receive data indicating locations and color characteristics of objects or persons in a scene and based on that information control LEDs or pcLEDs in an array to provide illumination adapted to the scene. Such data can be provided for example by an image sensor, or optical (e.g., laser scanning) or non-optical (e.g., millimeter radar) sensors. Such adaptive illumination is increasingly important for automotive (e.g., adaptive headlights), mobile device camera (e.g., adaptive flash), AR, VR, and MR applications such as those described below.

[0045] FIG. 5 schematically illustrates an example camera flash system 500 comprising an LED or pcLED array and an optical (e.g., lens) system 502, which may be or comprise an adaptive lighting system as described above in which LEDs or pcLEDs in the array may be individually operable or operable as groups. In operation of the camera flash system, illumination from some or all of the LEDs or pcLEDs in array and optical system 502 may be adjusted - deactivated, operated at full intensity, or operated at an intermediate intensity. The array may be a monolithic array, or comprise one or more monolithic arrays, as described above. The array may be a microLED array, as described above.

[0046] Flash system 500 also comprises an LED driver 506 that is controlled by a controller 504, such as a microprocessor. Controller 504 may also be coupled to a camera 507 and to sensors 508 and operate in accordance with instructions and profiles stored in memory 510. Camera 507 and LED or pcLED array and lens system 502 may be controlled by controller 504 to, for example, match the illumination provided by system 502 (i.e., the field of view of the illumination system) to the field of view of camera 507, or to otherwise adapt the illumination provided by system 502 to the scene viewed by the camera as described above. Sensors 508 may include, for example, positional sensors (e.g., a gyroscope and/or accelerometer) and/or other sensors that may be used to determine the position and orientation of system 500.

[0047] FIG. 6 schematically illustrates an example display system 600 that includes an array 610 of LEDs or pcLEDs that are individually operable or operable in groups, a display 620, a light emitting array controller 630, a sensor system 640, and a system controller 650. Array 610 may be a monolithic array, or comprise one or more monolithic arrays, as described above. The array may be monochromatic. Alternatively, the array may be a multicolor array in which different LEDs or pcLEDs in the array are configured to emit different colors of light, as described above. The array may therefore be or comprise a monolithic multicolor matrix of individually operable LED or pcLED light emitters, which may for example be microLEDs as described above. A single individually operable LED or pcLED or a group of adjacent such LEDs or pcLEDs in the array may correspond to a single pixel (picture element) in the display. For example, a group of three individually operable adjacent LEDs or pcLEDs comprising a red emitter, a blue emitter, and a green emitter may correspond to a single color-tunable pixel in the display. Similarly, to provide redundancy in the event of a defective LED or pcLED, a group of six individually operable adjacent LEDs or pcLEDs comprising two red emitters, two blue emitters, and two green emitters may correspond to a single color-tunable pixel in the display Array 610 can be used to project light in graphical or object patterns that can for example support AR/VR/MR systems.

[0048] Sensor input is provided to the sensor system 640, while power and user data input is provided to the system controller 650. In some embodiments modules included in system 600 can be compactly arranged in a single structure, or one or more elements can be separately mounted and connected via wireless or wired communication. For example, array 610, display 620, and sensor system 640 can be mounted on a headset or glasses, with the light emitting array controller and/or system controller 650 separately mounted.

[0049] System 600 can incorporate a wide range of optics (not shown) to couple light emitted by array 610 into display 620. Any suitable optics may be used for this purpose.

[0050] Sensor system 640 can include, for example, external sensors such as cameras, depth sensors, or audio sensors that monitor the environment, and internal sensors such as accelerometers or two or three axis gyroscopes that monitor an AR/VR/MR headset position. Other sensors can include but are not limited to air pressure, stress sensors, temperature sensors, or any other suitable sensors needed for local or remote environmental monitoring. In some embodiments, control input through the sensor system can include detected touch or taps, gestural input, or control based on headset or display position.

[0051] In response to data from sensor system 640, system controller 650 can send images or instructions to the light emitting array controller 630. Changes or modification to the images or instructions can also be made by user data input, or automated data input as needed. User data input can include but is not limited to that provided by audio instructions, haptic feedback, eye or pupil positioning, or connected keyboard, mouse, or game controller.

[0052] As noted above, AR, VR, and MR systems may be more generally referred to as examples of visualization systems. In a virtual reality system, a display can present to a user a view of a scene, such as a three-dimensional scene. The user can move within the scene, such as by repositioning the user’s head or by walking. The virtual reality system can detect the user’s movement and alter the view of the scene to account for the movement. For example, as a user rotates the user’s head, the system can present views of the scene that vary in view directions to match the user’s gaze. In this manner, the virtual reality system can simulate a user’s presence in the three-dimensional scene. Further, a virtual reality system can receive tactile sensory input, such as from wearable position sensors, and can optionally provide tactile feedback to the user. [0053] In an augmented reality system, the display can incorporate elements from the user’s surroundings into the view of the scene. For example, the augmented reality system can add textual captions and/or visual elements to a view of the user’s surroundings. For example, a retailer can use an augmented reality system to show a user what a piece of furniture would look like in a room of the user’s home, by incorporating a visualization of the piece of furniture over a captured image of the user’s surroundings. As the user moves around the user’s room, the visualization accounts for the user’s motion and alters the visualization of the furniture in a manner consistent with the motion. For example, the augmented reality system can position a virtual chair in a room. The user can stand in the room on a front side of the virtual chair location to view the front side of the chair. The user can move in the room to an area behind the virtual chair location to view a back side of the chair. In this manner, the augmented reality system can add elements to a dynamic view of the user’s surroundings.

[0054] FIG. 7 shows a generalized block diagram of an example visualization system 710. The visualization system 710 can include a wearable housing 712, such as a headset or goggles. The housing 712 can mechanically support and house the elements detailed below. In some examples, one or more of the elements detailed below can be included in one or more additional housings that can be separate from the wearable housing 712 and couplable to the wearable housing 712 wirelessly and/or via a wired connection. For example, a separate housing can reduce the weight of wearable goggles, such as by including batteries, radios, and other elements. The housing 712 can include one or more batteries 714, which can electrically power any or all of the elements detailed below. The housing 712 can include circuitry that can electrically couple to an external power supply, such as a wall outlet, to recharge the batteries 714. The housing 712 can include one or more radios 716 to communicate wirelessly with a server or network via a suitable protocol, such as WiFi.

[0055] The visualization system 710 can include one or more sensors 718, such as optical sensors, audio sensors, tactile sensors, thermal sensors, gyroscopic sensors, time-of-flight sensors, triangulation-based sensors, and others. In some examples, one or more of the sensors can sense a location, a position, and/or an orientation of a user. In some examples, one or more of the sensors 718 can produce a sensor signal in response to the sensed location, position, and/or orientation. The sensor signal can include sensor data that corresponds to a sensed location, position, and/or orientation. For example, the sensor data can include a depth map of the surroundings. In some examples, such as for an augmented reality system, one or more of the sensors 718 can capture a real-time video image of the surroundings proximate a user.

[0056] The visualization system 710 can include one or more video generation processors 720. The one or more video generation processors 720 can receive, from a server and/or a storage medium, scene data that represents a three-dimensional scene, such as a set of position coordinates for objects in the scene or a depth map of the scene. The one or more video generation processors 720 can receive one or more sensor signals from the one or more sensors 718. In response to the scene data, which represents the surroundings, and at least one sensor signal, which represents the location and/or orientation of the user with respect to the surroundings, the one or more video generation processors 720 can generate at least one video signal that corresponds to a view of the scene. In some examples, the one or more video generation processors 720 can generate two video signals, one for each eye of the user, that represent a view of the scene from a point of view of the left eye and the right eye of the user, respectively. In some examples, the one or more video generation processors 720 can generate more than two video signals and combine the video signals to provide one video signal for both eyes, two video signals for the two eyes, or other combinations.

[0057] The visualization system 710 can include one or more light sources 722 that can provide light for a display of the visualization system 710. Suitable light sources 722 can include any of the LEDs, pcLEDs, LED arrays, and pcLED arrays discussed above, for example those discussed above with respect to display system 600.

[0058] The visualization system 710 can include one or more modulators 724. The modulators 724 can be implemented in one of at least two configurations.

[0059] In a first configuration, the modulators 724 can include circuitry that can modulate the light sources 722 directly. For example, the light sources 722 can include an array of lightemitting diodes, and the modulators 724 can directly modulate the electrical power, electrical voltage, and/or electrical current directed to each light-emitting diode in the array to form modulated light. The modulation can be performed in an analog manner and/or a digital manner. In some examples, the light sources 722 can include an array of red light-emitting diodes, an array of green light-emitting diodes, and an array of blue light-emitting diodes, and the modulators 724 can directly modulate the red light-emitting diodes, the green light-emitting diodes, and the blue light-emitting diodes to form the modulated light to produce a specified image.

[0060] In a second configuration, the modulators 724 can include a modulation panel, such as a liquid crystal panel. The light sources 722 can produce uniform illumination, or nearly uniform illumination, to illuminate the modulation panel. The modulation panel can include pixels. Each pixel can selectively attenuate a respective portion of the modulation panel area in response to an electrical modulation signal to form the modulated light. In some examples, the modulators 724 can include multiple modulation panels that can modulate different colors of light. For example, the modulators 724 can include a red modulation panel that can attenuate red light from a red light source such as a red light-emitting diode, a green modulation panel that can attenuate green light from a green light source such as a green light-emitting diode, and a blue modulation panel that can attenuate blue light from a blue light source such as a blue light-emitting diode.

[0061] In some examples of the second configuration, the modulators 724 can receive uniform white light or nearly uniform white light from a white light source, such as a white-light lightemitting diode. The modulation panel can include wavelength-selective filters on each pixel of the modulation panel. The panel pixels can be arranged in groups (such as groups of three or four), where each group can form a pixel of a color image. For example, each group can include a panel pixel with a red color filter, a panel pixel with a green color filter, and a panel pixel with a blue color filter. Other suitable configurations can also be used.

[0062] The visualization system 710 can include one or more modulation processors 726, which can receive a video signal, such as from the one or more video generation processors 720, and, in response, can produce an electrical modulation signal. For configurations in which the modulators 724 directly modulate the light sources 722, the electrical modulation signal can drive the light sources 724. For configurations in which the modulators 724 include a modulation panel, the electrical modulation signal can drive the modulation panel.

[0063] The visualization system 710 can include one or more beam combiners 728 (also known as beam splitters 728), which can combine light beams of different colors to form a single multicolor beam. For configurations in which the light sources 722 can include multiple lightemitting diodes of different colors, the visualization system 710 can include one or more wavelength-sensitive (e.g., dichroic) beam splitters 728 that can combine the light of different colors to form a single multi-color beam.

[0064] The visualization system 710 can direct the modulated light toward the eyes of the viewer in one of at least two configurations. In a first configuration, the visualization system 710 can function as a projector, and can include suitable projection optics 730 that can project the modulated light onto one or more screens 732. The screens 732 can be located a suitable distance from an eye of the user. The visualization system 710 can optionally include one or more lenses 734 that can locate a virtual image of a screen 732 at a suitable distance from the eye, such as a close-focus distance, such as 500 mm, 750 mm, or another suitable distance. In some examples, the visualization system 710 can include a single screen 732, such that the modulated light can be directed toward both eyes of the user. In some examples, the visualization system 710 can include two screens 732, such that the modulated light from each screen 732 can be directed toward a respective eye of the user. In some examples, the visualization system 710 can include more than two screens 732. In a second configuration, the visualization system 710 can direct the modulated light directly into one or both eyes of a viewer. For example, the projection optics 730 can form an image on a retina of an eye of the user, or an image on each retina of the two eyes of the user.

[0065] For some configurations of augmented reality systems, the visualization system 710 can include an at least partially transparent display, such that a user can view the user’s surroundings through the display. For such configurations, the augmented reality system can produce modulated light that corresponds to the augmentation of the surroundings, rather than the surroundings itself. For example, in the example of a retailer showing a chair, the augmented reality system can direct modulated light, corresponding to the chair but not the rest of the room, toward a screen or toward an eye of a user. [0066] This disclosure describes metalenses that can be used with lighting devices, in particular lighting devices that use LED structures as light sources, such as the LED devices describe above. Metalenses disclosed herein are optical components with artificially designed ultra-thin (typically < 1mm) refractive surfaces made of sub -wavelength sized features that may vary in length and scale. The refractive surfaces may be referred to a “metasurfaces” and the subwavelength sized features forming the metasurface may be referred to as “nanostructures,” “meta-atoms”, or “nano-antennae”. The metasurface of the metalens imparts a phase and/or amplitude change to light incident on the metalens. The meta-atoms of the metasurface can be arranged so that the metalens creates the target phase profile for the desired optical effect in the light, for instance collimating, focusing, beam steering, polarizing, etc. Because metalenses are thin and planar, they can reduce the size of lighting devices. This disclosure describes metalenses that have a large area needed for use in lighting devices such as LED devices, and, in particular, metalenses that collimate light.

[0067] FIG. 8 is a cross-sectional view of a lighting device 800 having a metalens. Lighting device 800 includes a light source 810 and metalens 820. Lighting device 800 may be used in, for example, the LED devices described above.

[0068] Light source 810 may be, for example, and LED structure, for instance any of the LEDs, pcLEDs, LED arrays, or pcLED arrays disclosed above. Light source 810 emits light 830. In the examples disclosed herein, light 830 may be in the visible wavelength range (e.g., 400 nm - 700 nm). However, lighting device 800 may be used with light sources 810 emitting light in various wavelength ranges, for example, the infrared (“IR”) wavelength range (e.g., 780 nm - 1 mm) including near IR and short-wave IR, ultraviolet wavelength range (e.g., lOOnm - 400 nm), or a wavelength range defined by the wavelengths of light 830 emitted by light source 810 that are within 1/15 of the wavelength of light 830 having the peak intensity.

[0069] Metalens 820 is spaced apart from light source 810 and positioned so as to receive light 830 emitted from light source 810. For example, the metalens 820 may be spaced apart from the light source 810 at a distance that is the same as or close to the focal length of the metalens. Metalens 820 includes an ultra-thin (< 1 mm) metasurface 828. The metasurface 828, including an arrangement of meta-atoms 825, is described below. The metasurface 828 is disposed on a substrate 827, which may be transparent and may have a sub-mm thickness, such that the metalens 820 has a thickness that is less than 1 mm. [0070] Metalens 820 may be planar, as shown, and may have dimensions significantly larger than those of the light source as measured in a plane parallel to the plane of the light source. For example, the light source 810 may be and LED structure, and metalens 820 may be 2 to 3 or more times the size of the LED structure. In some instances, metalens 820 may have an area that is relatively large, for example, a diameter of the metalens in a plane parallel to the plane of the light source may be between 1 mm - 10 mm. Light 830 emitted from the light source 810 is incident upon the metalens 820. Metalens 820 functions as a lens, e.g., it focuses, collimates, or otherwise redirects light 830. FIG. 8 illustrates metalens 820 having in a configuration that collimates light 830 incident upon metalens 820, as shown by light 840 exiting the upper surface 829 of the metalens 820.

[0071] Metasurfaces, such as metasurface 828, include or may be formed from an array of metaatoms 827. In general, meta-atoms are in the form of nanoscale features that have dimensions on the order of, or less than, the wavelengths of light the metalens is to modulate. The meta-atoms may be formed directly on or integral with a surface of the substrate (827). The modulation of the phase and amplitude of the light emitted by the LED structure through a metalens can be controlled by the architecture of the metasurface, which is set by certain parameters. These parameters include (i) the size and shape of the meta-atoms, and how the size and shape of the meta-atoms vary with specific position across the metalens, (ii) the arrangement of the specific position of each meta-atom on the substrate, including the distance between meta-atoms, and how the arrangement of the specific position varies across the metalens, and (iii) the material used to form the metalens. For metalenses formed with high refractive index material, for instance dielectric material having minimal absorption (in the visible wavelength range) such as metal oxides, the parameters (i) and (ii) are used to further control the redirection of light through the metalens.

[0072] FIGS. 9A and 9B illustrate parameters (i) and (ii) for an example metalens 900. FIG. 9A illustrates a perspective view of a portion of example metalens 900. FIG. 9B is a cross-sectional view of a segment of the metalens 900 shown in FIG. 9A.

[0073] As shown in FIG. 9A, the example metalens 900 includes meta-atoms in the shape of cylinders 920, which may also be referred to as pillars or nano-antennas. There are numerous pillars 920 on the substrate 910, which are arranged in an array. For example, a metalens may have an array of pillars 920 arranged to form nano-gratings in concentric rings about a central optical axis of the metalens, with the long axes of the pillars arranged perpendicularly to the plane of the array. In some metasurfaces, for example, the width of the concentric ring in the plane of the metalens may change as a function of radial distance from the central optical axis. [0074] FIG. 9B shows a cross sectional view of three of the pillars 920, along a line positioned through the middle of the three pillars 920. Viewing FIG. 9B, each pillar 920 can be characterized by a height H and a diameter D. In general, the height H and diameter D of the pillars are chosen so as to attain the target phase profile for the desired optical effect. Generally, for metalenses configured for use in the visible wavelength range, diameters D of pillars may be between, for example, about 40 nm and about 500 nm and heights may be between, for example, about 200 nm and 2000 nm. In general, across the array, the height H may vary between adjacent pillars 920, as shown in the segment of FIG. 9B., such as between adjacent pillars 920 along lines extending radially from the central optical axis of the metalens. The height H may, alternatively or additionally vary between pillars 920 positioned in different regions of the array. Alternatively, the height H may be the same across the entire array of the metalens. An example is shown in FIG. 9C, which is a cross-sectional view of a small segment of a metalens 990 having a different configuration than metalens 900. Metalens 990 includes pillars 992 on substrate 991. In metalens 990, the height H of all of the pillars 929 may be held at a constant value throughout the metasurface, and only the diameters D of the pillars 920 varied. Such a configuration may allow for easier manufacturing of the metalens. In particular, the diameter D may vary between adjacent pillars 992 along lines extending radially from the central optical axis of the metalens, or between certain regions of the array. Alternatively, the diameter D may be the same across the entire array of the metalens.

[0075] In the examples shown in FIGS. 9B and 9C, meta-atoms such as pillars 920, 992 are positioned as part of a unit cell 930, 993 on the metasurface. The pitch P (or center - to - center spacing) is the distance between adjacent pillars of the array along lines extending radially from the central optical axis. In a metalens used with light having wavelengths in the visible light range, the pitch P may be, for example, less than 280 nm, for example, between 220 nm and 260 nm. The pitch P may vary between pillars, or regions of pillars, or may be the same for the entire metalens. Pillars 920, 929 may be arranged in an array to form, as an example, nanogratings in concentric rings about a central optical axis of the metalens, with, as shown in FIGS. 9A, 9B and 9C with the long axes of the pillars arranged perpendicularly to the plane of the array. In such an arrangement, the period P may be arranged to stay the same across the metalens. Alternatively, the period P may be arranged so that width of each concentric ring in the plane of the metalens decreases or increases as a function of radial distance from the central optical axis. That is, the period P may decrease or increase with increasing radial distance from the central axis.

[0076] For metalenses to be used with LED devices in the visible wavelength range, the materials used to form the metasurface may have minimal absorption in the visible range and for instance a high refractive index, and may include dielectric materials, such as dielectric oxides (e.g., metal oxides), e.g., TiCh, Nb2Os, Ta2Os, SiNx, and a-Si. The substrate 910 may be transparent, and may be formed from, for example, sapphire.

[0077] One of the challenges for metalenses is formulating a metasurface that is effective over a range of wavelengths while also having a relatively larger size, for example, having a lens diameter of greater than 1 mm, e.g., 1 mm - 10 mm while maintaining a high efficiency, for example, having a high transmittance across the full range of wavelengths that the metalens is required to modulate for the given application.

[0078] FIG. 10 illustrates transmission results for sample metalenses with relatively larger areas over the visible wavelength range. The parameters used in forming the sample metalenses are below in Table 1. Four sample metalenses were prepared. A first with the parameters of sample #A and having a silica overcoat. A second with the parameters of sample #A but without the silica overcoat. A third with the parameters of sample #B and having a silica overcoat. A further with the parameters of sample #B but without a silica overcoat:

[0079] FIG. 10 is a graph 1000 showing the measured transmission of all four samples across the visible wavelength range from 400 nm to 800 nm. Lines 1010 and 1020 are the measured transmission of the two sample metalenses #1 and #2 having silica overcoats. The measured transmission 1010 and 1020 is essentially the same for both of these metalenses. Lines 1030 and 1040 are the measured transmission of the metalenses #3 and #4, without silica overcoats. Viewing graph 1000, the silica overcoat improves transmission. While the silica overcoats enhance overall transmission, looking at graph 1000, the inventors have found that transmission decreases significantly at wavelengths less than 500 nm for all four samples. The decrease in transmission in this region of the visible wavelength range also decreases overall transmission of the metalens samples.

[0080] To identify the source of the transmission loss, the inventors first simulated the transmission results with simulated metalenses having the parameters of the samples. Dots 1060 are a plot of the transmission values of the simulated data for metalenses having the parameters of sample #1 - #4. Viewing Dots 1060, the simulation was able to represent the transmission loss that occurred in the prepared samples. The inventors recognized that the source of the transmission loss is certain electro-magnetic resonances occurring within the structure of the metasurface. These electro-magnetic resonances, which are referred to as Mie resonances or morphology-dependent resonances, act to absorb energy (light) at the wavelengths the resonance occur within the structure, and hence lower transmission. While Mie resonances have been utilized and purposely incorporated in certain metasurface designs, the inventors recognized that to improve transmission, the Mie resonances need to be avoided within the metasurface (i.e., not occur in the metasurface) for wavelengths of light the metasurface will modulate. That is, transmission can be enhanced for metasurfaces that do not experience Mie resonances. In particular, the Mie resonances need to be avoided in dielectric metasurface for collimating light, in particular light in the visible wavelength ranges, to achieve high transmission across all wavelengths.

[0081] FIG. 11A is a graph showing the simulated transmission of 4 different metasurfaces at a wavelength of 450 nm for a range of pillar diameters D. The transmission shown by graph 1106 corresponds to the simulated transmission for metasurface of samples #l-#4 above, in which the pillar height H is a constant 600 nm, the pitch P is a constant 280 nm, and pillar diameters D are varied from 70 - 240 nm. The transmission shown by graph 1108 corresponds to the simulated transmission for metasurface of sample #1 - #4 above, except that the pillar height H is held constant at 800 nm. Viewing FIG. 11 A, Mie resonances lead to significant absorption, and reduced transmission at pillar diameters D greater than approximately 150 nm. Repeating the simulation for metasurfaces having pillars with either a lower constant height, i.e., 400 nm line 1104, or higher constant height, i.e., 1000 nm, line 1110, while keeping the other parameters the same, does not significantly improve transmission.

[0082] FIG. 1 IB is a graph of the relative phase of light as a function of pillar diameter D at 450 nm for metasurfaces with the same parameters as shown in FIG. 11 A, that is, a pitch P of 280 nm and four different heights 400 nm (line 1114), 600 nm (line 1116), 800 nm (line 1118), and 1000 nm (line 1101). To achieve a metalens that produces the desired optical effect, e.g., collimates light, a phase change over the diameters of 0 to 2% is needed, where 2rc is indicated with dashed line at 1. Comparing FIGS. 11A and 1 IB, the full 0 to 2n phase change cannot be achieved with the pillar diameters D needed and also prevent transmission loss in the metasurface. That is, if the pillar diameters D are maintained below the 140 nm required to prevent Mie resonances in the metasurface that lead to transmission loss, the full 0 to 2TT phase change cannot be achieved. [0083] To avoid the Mie resonances in metalenses for the applications of samples #1 - #4, inventors have found that reducing the pitch P to below approximately 240 nm, for example to 220 nm. Reducing the pitch P allows pillar diameters D to achieve a full 0 to 2n phase change without the metasurface having resonances that cause transmission loss.

[0084] FIG. 12 illustrates simulated transmission data for an example metalens in which the height H of the pillars is held constant at 800 nm and the pitch (period) P is reduced to 220 nm at three wavelengths 450 nm, 532 nm, and 650 nm. The transmission is shown at 450 nm (line 1204), 532 nm (line 1205) and 650 nm (line 1206). With the pitch P reduced from 280 nm to 220 nm, the simulated data show that no resonances for RGB frequencies in the pillar diameter D of less than approximately 190 nm, more specifically, less than 170 nm. Thus, although reducing the pitch P puts the pillars closer together on the metasurface, Mie resonances are avoided and the pillar diameters D only need to less than approximately 170 nm, for example vary between ~40 nm - ~ 170 nm, to achieve full 0 to 2n phase change. If the pitch P is somewhat larger, for instance, 240 nm, the pillar diameters D can be somewhat larger, for instance 190 nm or less, without the metalens exhibiting Mie resonances. In general, the pitch P may be less than 260 nm, the pillars vary in height to achieve the desired optical effect, and, for instance, are in a range less than 190 nm, and the heights H can vary between 200 and 2000 nm, but more practically between 400 nm and 1000 nm.

[0085] FIG. 13 shows a plot of simulated transmission (1310) and reflection (1320) data across the visible wavelength range from 400 to 750 nm for a metalens with a metasurface structure that avoids Mie resonances. The metalens of FIG. 13 collimates light, and has an overall diameter (i.e., lens diameters) of 5 mm, and a focal length of 1.8 mm. The unit cell period (pitch P) is 220nm, and diameters of the cylindrical pillars vary between 40 nm to 170 nm for a full 2n phase variation. The pillar heights are fixed at 800nm. The substrate is Coming glass with a refractive index (“RI”) of 1.513 and pillar (metasurface) dielectric material is bt Os with RI of 2.31. The metalens includes a protective silica overcoat layer of a few 100s nm, for example, between 200 nm and 300 nm, on top of the pillars which also improves transmission into air. The simulations predict a > 90% transmission for the full metalens for the majority of the visible range. This metalens is an improvement from previous metalens samples, which had a measured a lower measure transmission, specifically in the blue region (as shown in FIG. 10).

[0086] FIG. 14A is a plan view of a metalens having a metasurface structure that avoids Mie resonances. FIG. 14B is an expansion of region 14B marked in FIG. 14A. FIG. 14C is an expansion of region 14C marked in FIG. 14A.

[0087] The metalens 1400 of FIG. 14A has a central optical axis extending through the center (marked 1410) of the metalens 1400 perpendicular to the plane of the metalens 1400. The pillars 1450 (FIGS. 14B and 14C) are arranged in concentric rings about the central optical axis of the metalens, with the long axes (height H) of the pillars 1450 arranged perpendicularly to the plane of the array, thus FIGS. 14B and 14C show the tops of the pillars 1450, with the varying diameters D. The diameter D of the pillars is varied radially (e.g., radius 1460) from the central optical axis 1410 between adjacent pillars to affect the phase change in light that enters the metalens. FIGS. 14B and 14C show the pillar diameter D changing monotonically such that the phase goes from 0 to 2 and the concentric rings form a grating which collimates light entering the metalens 1400 from a light source.

[0088] FIG. 15 illustrates determination of pillar diameters as a function of position in the metalens for a phase variation of 0 to 2K (shown in graph 1501). <I> (x, y) is determined, in this example for a focal length f of 1.8 mm and at a wavelength of 532 nm.

[0089] Metalenses disclosed herein can be manufactured using methods known in the art. For instance, metalenses may be prepared using sputtering (physical vapor deposition) or chemical vapor deposition to form a homogenous layer of the metasurface material. Immersion DUV, or alternatively nanoimprinting patterning techniques can be subsequently used to pattern the layer to form the array of pillars, followed by anisotropic etching in which a hard mask may be used to have a defined etch stop, leading to a well-defined layer thickness (e.g., pillar height H).

[0090] This disclosure is illustrative and not limiting. Further modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A lighting device comprising: a light source configured to emit light having wavelengths within a wavelength range; and a metalens positioned to receive the light, the metalens including a metasurface disposed on a substrate, the metasurface configured to affect a phase of the light received by the metalens from the light source to produce an optical effect in the light and configured to not exhibit Mie resonances within the wavelength range of the light.

2. The lighting device of claim 1, wherein the metasurface comprises an array of metaatoms, the meta-atoms extending radially around an optical axis of the metalens, the meta-atoms spaced apart at a pitch, the pitch having a value less than a shortest wavelength in the wavelength range, the meta-atoms arranged and varying in size to affect a phase change of light without metasurface exhibiting Mie resonances.

3. The lighting device of claim 2, wherein the meta-atoms comprise pillars having a height and a diameter, the height of the pillars is a constant value over the metasurface, and a value of the pitch is set so the diameter of the pillars is varied radially between adjacent pillars to affect the phase change of the light without the metasurface exhibiting Mie resonances.

4. The lighting device of claim 3, wherein the wavelength range comprises wavelength in a visible light range, the optical effect is to collimate the light, the pitch is less than 240 nm, and the diameter of the pillars is varied to affect the phase change between 0 and 2n in the light.

5. The lighting device of claim 3, wherein the diameter is less than 190 nm.

6. The lighting device of claim 3, wherein the pitch is 220 nm and the diameter of the pillars varies between 40 nm and 170 nm.

7. The lighting device of claim 1, wherein the metalens has a lens diameter on a side facing the light source of 1 mm or more.

8. The lighting device of claim 7, wherein the lens diameter is 5 mm.

9. The lighting device of claim 1, wherein the optical effect is collimating the light.

10. The lighting device of claim 1, wherein the light source is an LED structure emitting light in the visible wavelength range.

11. The lighting device of claim 10, wherein the LED structure is a pcLED array.

12. The lighting device of claim 1, wherein the metalens comprises a dielectric material.

13. The lighting device of claim 12, wherein the dielectric material is a metal oxide.

14. The lighting device of claim 1, wherein a thickness of the metalens is less than 1 mm.

15. A metalens comprising: a substrate; and a metasurface disposed directly on the substrate and comprising a dielectric material, the metasurface comprising an array of pillars extending radially from an optical axis of the metasurface, the pillars having a height that is a fixed value and a diameter that varies, the pillars spaced apart at a pitch of 240 nm or less.

16. The metalens of claim 15, wherein the diameter of the pillars varies to affect a phase change between 0 and

in light between the wavelengths of 400 nm and 700 nm.

17. The metalens of claim 16, wherein the diameter of the pillars is less than 170 nm.

18. The metalens of claim 16, wherein the pitch is 220 nm and the diameter of the pillars varies between 40 nm and 170 nm.

19. The metalens of claim 16, wherein the pitch is 240 nm and the diameter of the pillars is less than 190 nm.

20. The metalens of claim 15, wherein the dielectric material is a metal oxide.