Magic Leap Patent | Projector with scanning array light engine

Patent: Projector with scanning array light engine

Publication Number: 10175564

Publication Date: 2019-01-08

Applicants: Magic Leap

Abstract

A projector assembly includes a light emitting diode (LED) array, wherein the LED array has an array axis, wherein the LED array includes a plurality of LEDs arranged along the array axis, and wherein the plurality of LEDs are individually addressable. The projector assembly includes a rotatable actuator supporting the LED array, wherein the rotatable actuator has a rotation axis, and wherein the rotation axis and the array axis are parallel. The projector assembly includes a collimator positioned in optical communication with the LED array for collimating light emitted from the plurality of LEDs and a set of imaging optics positioned in optical communication with the collimator for focusing collimated light and forming a first image of the LED array at a distance, wherein the first image includes a first axis corresponding to the array axis and a second axis orthogonal to the rotation axis.

Background

Image projectors can take many forms and use a variety of different technologies, which range in both cost and complexity. For example, many common projectors used in office, conference, and home theater systems for video projection make use of 3 color light recombination (red, green, blue) for full color video. In liquid crystal display (LCD) projectors, light from a lamp is separated for each of the red, green, and blue components and passed through LCD gates including a plurality of pixels for blocking or allowing the light to pass to generate an output light pattern. Digital light processing (DLP) and liquid crystal on silicon (LCOS) projectors use similar technology but respectively make use of micromirror and reflective active matrix liquid-crystal elements for generating the output light patterns instead of LCD gates. Due to the need for including optical elements for each of the 3 colors, these systems may be large and overly complex.

Summary

The present disclosure relates to image projection. In particular, the present disclosure relates to a light emitting diode based image projector. Described herein are LED-based image projection systems and related projection methods. The systems and methods described herein make use of an array of LEDs, which output light that is projected using optical elements to form images at a distance. The size and/or number of LEDs in the LED array may be reduced as compared to other LED projection technologies by placing the LED array on a movable actuator, such as a rotatable actuator, so that images of the LED array at different positions can be generated and combined to form a composite frame. For example, as the LED array is rotated as a function of time, a sequence of images of the array can be generated. When done at a rapid enough rate, a section by section composite frame, similar to a progressive scan frame, can be produced, and this process can be repeated to project a video image.

In a first aspect, projector assemblies are provided. In a specific embodiment, a projector assembly comprises a light emitting diode (LED) array such as an LED array that has an array axis and includes a plurality of LEDs arranged along the array axis. The plurality of LEDs can be individually addressable. The projector assembly further comprises a movable actuator supporting the LED array such as a rotatable actuator that has a rotation axis that is parallel to the array axis or a translatable actuator that has a translation axis perpendicular to the array axis and a set of imaging optics positioned in optical communication with the LED array for forming a first image of the LED array at a distance. For example, the first image may include a first axis corresponding to the array axis and a second axis orthogonal to the rotation axis or parallel to the translation axis. Optionally, output intensities of each of the plurality of LEDs are independently controllable.

A variety of LED arrays are useful with the projector assembles described herein. For example, in some embodiments, the LED array comprises a one-dimensional LED array. Optionally, the LED array comprises a two-dimensional LED array. Useful LED arrays include LED arrays having any practical number of elements. For example, in some embodiments, the LED array includes about 800 pixels, about 1024 pixels, about 1280 pixels, about 1440 pixels, about 1600 pixels, about 1920 pixels, about 2560 pixels, about 3840 pixels, about 7680 pixels, or more than about 7680 pixels. Optionally, each pixel corresponds to one or more corresponding LEDs of the LED array.

In embodiments, the plurality of LEDs may generate light of any suitable color or wavelength. For example, in some embodiments, the plurality LEDs include a first plurality of LEDs for producing light including a first wavelength, a corresponding second plurality of LEDs for producing light including a second wavelength different from the first wavelength, and a corresponding third plurality of LEDs for producing light including a third wavelength different from the first wavelength and the second wavelength. In this way, full color images may be generated by combining light from LEDs of three different colors. For example, in some embodiments, a set of three corresponding LEDs make up a pixel of the LED array. Optionally, a set of three corresponding LEDs includes one LED from the first plurality of LEDs, one LED from the second plurality of LEDs, and one LED from the third plurality of LEDs. Other configurations are possible, including where multiple LEDs from a plurality of LEDs are included in a set of LEDs making up a pixel.

Optionally, one of the first, second, or third wavelengths is about 650 nm. Optionally, one of the first, second, or third wavelengths is about 520 nm. Optionally, one of the first, second, or third wavelengths is about 450 nm. Optionally, the light of the first, second, or third wavelength is or peaks at about 650 nm. Optionally, the light of the first, second, or third is or peaks at about 520 nm. Optionally, the light of the first, second, or third is or peaks at about 450 nm. Other color/wavelength combinations are possible.

In some embodiments, the first plurality of LEDs, the second plurality of LEDs, and the third plurality of LEDs include a same number of LEDs. However, in other embodiments, each of the first, second and third plurality of LEDs may include different numbers of LEDs. For example, in some embodiments, the first plurality of LEDs includes a different number of LEDs as the second plurality of LEDs, the third plurality of LEDs or both the second plurality of LEDs and the third plurality of LEDs.

The LEDs in the array may be arranged according to any preferred configuration. For example, in some embodiments, the first plurality of LEDs, the second plurality of LEDs, and the third plurality of LEDs are uniformly distributed along the array axis. Optionally, the first plurality of LEDs are spatially grouped. Optionally, the second plurality of LEDs are spatially grouped. Optionally, the third plurality of LEDs are spatially grouped. Grouping of LEDs of a common wavelength/color may be useful for some embodiments, including embodiments where generation of spatially distinct single-color images is desired. In some embodiments, each LED in the second plurality of LEDs is positioned adjacent to at least one corresponding LED in the first plurality of LEDs and at least one corresponding LED in the third plurality of LEDs.

LEDs included in the array may take on any suitable dimension. For example, in embodiments, each of the plurality of LEDs has a lateral dimension selected between about 0.5 .mu.m and about 5 .mu.m. The LED array itself may also take on any suitable dimension. In some embodiments, the LED array has a width axis orthogonal to the array axis, and wherein the width axis corresponds to the second axis. For example, in some embodiments, the LED array has a length along the array axis selected between about 100 .mu.m and about 10000 .mu.m. Optionally, the LED array has a length along the width axis between about 0.5 .mu.m and about 100 .mu.m.

LEDs of any suitable switching speed may be used with the methods and assemblies described herein. It will be appreciated that a switching speed as fast as or faster than a desired frame rate for a video image may be useful with some embodiments. Optionally, each of the plurality of LEDs are switchable at a frequency greater than or about 30 Hz, greater than or about 60 Hz, greater than or about 120 Hz, greater than or about 240 Hz, greater than or about 1 kHz, greater or than about 1 MHz, or between about 10 Hz and about 10 MHz.

In embodiments, supporting the LED array by a rotatable actuator is useful to allow the LED array to generate outputs that may be spatially separated. In embodiments, the rotatable actuator comprises a microelectromechanical element. Optionally, the rotatable actuator comprises a piezoelectric element. The rotatable actuator may be rotatable to any suitable number of positions or to any suitable angle. In some embodiments, the rotatable actuator is controllable to a plurality of distinct positions parallel to the array axis including about 600, about 768, about 720, about 800, about 900, about 1024, about 1200, about 1080, about 1440, about 1600, about 2160, about 4230, more than about 4230 distinct positions parallel to the array axis, or between about 100 and about 100000 positions parallel to the array axis.

Optionally, the rotatable actuator has a length along the array axis that is about equal to a lateral dimension of the LED array along the array axis. Optionally, the LED array has a width axis orthogonal to the array axis. In embodiments, the rotatable actuator has a rotation angle around the rotation axis corresponding to an angle between an optical axis of the collimator or the set of imaging optics and the width axis, such as a rotation angle that is continuously or discretely controllable between about 45.degree. and about +135.degree.. It will be appreciated that, in some embodiments, rotation of the rotatable actuator about the rotation axis causes a displacement of the LED array orthogonal to the rotation axis.

In embodiments, supporting the LED array by a translatable actuator is useful to allow the LED array to generate outputs that may be spatially separated. In embodiments, the translatable actuator comprises a microelectromechanical element. Optionally, the translatable actuator comprises a piezoelectric element. The translatable actuator may be translatable to any suitable number of positions. In some embodiments, the translatable actuator is controllable to a plurality of distinct positions parallel to the array axis including about 600, about 768, about 720, about 800, about 900, about 1024, about 1200, about 1080, about 1440, about 1600, about 2160, about 4230, or more than about 4230 distinct positions parallel to the array axis.

Optionally, the translatable actuator has a length along the array axis that is about equal to a lateral dimension of the LED array along the array axis. Optionally, the LED array has a width axis orthogonal to the array axis. In embodiments, the translatable actuator is translatable along the translation axis continuously or discretely.

In a specific embodiment, the LED array outputs a one-pixel wide output and rotation of the LED array about the rotation axis or translation of the LED array along the translation axis generates a two-dimensional optical output corresponding to a composite of multiple one-pixel wide outputs. For example, the two-dimensional optical output may be imaged by the set of imaging optics to generate the first image.

Optionally, the set of imaging optics includes a collimator, which may be useful for generating collimated light from the LED array. In embodiments, the collimator comprises a lens or a mirror. Optionally, the collimator is positioned to receive light generated by the plurality of LEDs and output parallel light rays. In some embodiments, the collimator comprises an optical element that is contoured to output parallel or substantially parallel light rays from the plurality of LEDs as the rotatable actuator is moved, such as about the rotation axis or along a translation axis. Optionally, the collimator comprises a plurality of collimation elements each positioned to receive light generated by a subset of the plurality of LEDs and output parallel or substantially parallel light rays.

In embodiments, the collimator may include optical coatings or filters. For example, in some embodiments, the collimator includes a reflective or anti-reflective coating. Optionally, the collimator includes a polarizer.

Other optical elements are useful with the set of imaging optics. For example, in some embodiments, the set of imaging optics includes one or more lenses, mirrors, or filters. Optionally, the set of imaging optics focuses light generated by the plurality of LEDs to a focal length of between about 1 mm and 1 m. Optionally, optical elements of the set of imaging optics includes one or more reflective or anti-reflective coatings or a polarizer.

In some embodiments, a projector assembly may include one or more additional LED array for generating one or more additional images. Such images may optionally be spatially offset and may correspond to the same or different output intensities. In some embodiments, a projector assembly may further comprise a second LED array, such as a second LED array that has a second array axis and that includes a second plurality LEDs, such as individually addressable LEDs, that are arranged along the second array axis; and a second movable actuator supporting the second LED array, such as a rotatable actuator that has a second translation axis that is parallel to the second array axis or a translatable actuator that has a second translation axis that is perpendicular to the array axis. In some embodiments, the second LED array is positioned in optical communication with the set of imaging optics. For example, the second LED array may be positioned in optical communication with a collimator, such as a collimator that collimates light emitted from the second plurality of LEDs. Optionally, the set of imaging optics forms a second image of the second LED array at a distance, such as a second image that includes a third axis corresponding to the second array axis and a fourth axis orthogonal to the second rotation axis or parallel to the second translation axis.

Various configurations of the first LED array and the second LED array are possible. For example, the second array axis and the first array axis may optionally be parallel. Optionally, the second array axis and the first array axis may be perpendicular. Depending on the particular configuration, the LED array and the second LED array may optionally have different lateral dimensions and/or include different numbers of LEDs.

In some embodiments, the first image generated by the first LED array corresponds to a first depth field and the second image generated by the second LED array corresponds to a second depth field. In this way, the projector assembly may generate multiple images of a same scene, but featuring different depth planes, and be useful for generating an image that may have depth information. If using two projector assemblies, each assembly may generate an image from a slightly different perspective, making the depth fields useful for generation of a three dimensional display.

In some embodiments, the first image and the second image at least partially spatially overlap. In this way, the two images may complement one another, and may, for example, be useful for improving a video refresh rate. Optionally, the first image and the second image are spatially offset.

In another embodiment, multiple images may be generated using a single LED array, such as multiple spatially offset images. For example, in some embodiments, a projector assembly may further comprise a translation stage, for generating a relative translation between the LED array and the set of imaging optics. In this way, the LED array may be translated to a second position so that a second image may be generated. Optionally, the translation stage comprises a microelectromechanical element. Optionally, the translation stage comprises a piezoelectric element. In embodiments, the relative translation is along an axis perpendicular to the rotation axis or parallel to the translation axis. It will be appreciated that the relative translation may be useful for forming a second image of the LED array in a translated position.

Different configurations may be useful for generating the relative translation. For example, in some embodiments, translation stage is in mechanical communication with the rotatable actuator for translating the movable actuator and the LED array relative to the set of imaging optics. Optionally, the translation stage is in mechanical communication with the collimator for translating the set of imaging optics relative to the LED array.

Other components may be useful with the projector assemblies and methods described herein. For example, one or more waveguides or diffractive elements may be used, such as to aid in a viewer seeing the images generated by the projector assembly. For example, in some embodiments, a projector assembly may further comprise a first diffractive optical element positioned in optical communication with the set of imaging optics for receiving the first image of the LED array and generating first diffracted light; a waveguide positioned in optical communication with the first diffractive optical element for receiving the first diffracted light and transmitting the first diffracted light by total internal reflection; a second diffractive optical element positioned within or on the waveguide for generating second diffracted light from the first diffracted light; and a third diffractive optical element positioned in optical communication with the second diffractive element for third generating diffracted light from the second diffracted light. Additional details regarding the use of waveguides and diffractive elements for generating a display of the images generated by a projector assembly may be found in U.S. Provisional Application 62/377,831, filed Aug. 22, 2016, which is hereby incorporated by reference in its entirety.

In another embodiment, a projector assembly may comprise a light emitting diode (LED) array, such as an LED array has an array axis and includes a plurality of LEDs, which may be individually addressable, arranged along the array axis; a movable actuator supporting the LED array, such as a rotatable actuator that has a rotation axis that is parallel to the array axis or a translatable actuator that has a translation axis that is perpendicular to the array axis; a set of imaging optics positioned in optical communication with the LED array for collecting light emitted by the plurality of LEDs and forming one or more images of the LED array at a distance, such as one or more images that include a first axis corresponding to the array axis and a second axis orthogonal to the rotation axis or parallel to the translation axis.

In some embodiments, the set of imaging optics may not include a collimator. When a collimator is not included, directional information for light generated by the LED array may be retained in the projected image, which may be useful for some embodiments. For example, it will be appreciated that retaining directional information may be useful for light field applications, where direction, phase, and/or amplitude/intensity may be retained in order to generate a three-dimensional or four-dimensional image. Optionally, the plurality of LEDs each have independently controllable output amplitudes. Optionally, the set of imaging optics includes one or more electro-optic elements for controlling and/or retaining a phase of light emitted by the plurality of LEDs. Optionally, the set of imaging optics includes one or more elements for controlling and/or retaining directional information for light emitted by the plurality of LEDs. Optionally, a rotatable actuator controls a direction of light generated by the LED array.

In another aspect, methods are described for generating images, such as by using a projector assembly described herein. In one example, a method embodiment of this aspect may comprise creating a first partial image using a projector assembly, moving a movable actuator of the projector assembly to move the LED array of the projector assembly to a second position; and creating a second partial image using the projector assembly. Optionally, the first partial image and the second partial image are spatially offset and together form a first composite image.

In some embodiments, the movable actuator comprises a rotatable actuator. In some embodiments, a method of this aspect may further comprise rotating the rotatable actuator one or more times and creating one or more corresponding additional partial images, such as where the one or more corresponding additional partial images are each spatially offset from other partial images and together form the first composite image. Optionally, rotating the rotatable actuator includes rotating the rotatable actuator by a discrete angle. Optionally, rotating the rotatable actuator includes rotating the rotatable actuator continuously.

In some embodiments, the movable actuator comprises a translatable actuator. In some embodiments, a method of this aspect may further comprise translating the translatable actuator one or more times and creating one or more corresponding additional partial images, such as where the one or more corresponding additional partial images are each spatially offset from other partial images and together form the first composite image. Optionally, translating the translatable actuator includes translating the translatable actuator by a discrete distance. Optionally, translating the translatable actuator includes translating the translatable actuator continuously.

In some embodiments, creating the first partial image, moving the movable actuator, and creating the second partial image are repeated at a rate of about 30 Hz, about 60 Hz, about 120 Hz, about 240 Hz, greater than about 240 Hz, or between about 10 Hz and 480 Hz. In this way, methods of this aspect may be used for generating video images.

Optionally, the projector assembly may include a translation stage for generating relative translations between the LED array and the set of imaging optics. In some embodiments, a method of this aspect may further comprise generating a relative translation between the LED array and the set of imaging optics such that the LED array is translated to a translated relative position; creating a third partial image, such as by generating a third light using the LED array at the translated relative position and imaging the third light by the set of imaging optics to form the third partial image; moving the movable actuator to move the LED array to a translated and moved relative position; creating a fourth partial image, such as by generating a fourth light using the LED array at the translated and moved relative position and imaging the fourth light by the set of imaging optics to form the fourth partial image, so that the third partial image and the fourth partial image are spatially offset and together form a second composite image. Optionally, the first composite image corresponds to a first depth field and the second composite image corresponds to a second depth field.

Optionally, the projector assembly may include two or more LED array, such as two or more LED array each having independent array axes, and independently include a pluralities of LEDs, where each LED element is individually addressable, arranged along the respective array axes; and two or more movable actuator each respectively supporting an LED array. Each LED array may be positioned in optical communication with a set of imaging optics so that images of each LED array may be formed at a distance.

Optionally, a method of this aspect may comprise creating a third partial image, such as by generating third light using a second LED array at a third position, and imaging the third light by the set of imaging optics to form the third partial image; moving a second movable actuator to move the second LED array to a fourth position; creating a fourth partial image, such as by generating fourth light using the second LED array at the fourth position and imaging the fourth light by the set of imaging optics to form the fourth partial image. Optionally, the third partial image and the fourth partial image are spatially offset and together form a second composite image. Again, it will be appreciated that different composite images may correspond to different depth fields.

Optionally, projector assemblies useful with the methods described herein may further comprise a first diffractive optical element positioned in optical communication with the set of imaging optics for receiving the first image of the LED array and generating diffracted light; a waveguide positioned in optical communication with the first diffractive optical element for receiving the diffracted light and transmitting the diffracted light by total internal reflection; a second diffractive optical element positioned within or on the waveguide for generating diffracted light; and a third diffractive optical element positioned in optical communication with the second diffractive element for generating diffracted light. Optionally, a method of this aspect may further comprise diffracting at least a portion of the first composite image using the first diffractive optical element to generate a diffracted image, such as a diffracted image that is received by the waveguide; transmitting the diffracted image using the waveguide; diffracting at least a portion of the diffracted image using the second diffractive optical element to generate an expanded image; and diffracting at least a portion of the expanded image using the third diffractive optical element to generate an output image. In this way, images generated by the projector assembly may be displayed for a viewer.

In another aspect, projector assemblies are provided. In an embodiment, a projector assembly comprises a LED array, wherein the LED array has an array axis, wherein the LED array includes a plurality of LEDs arranged along the array axis, and wherein the plurality of LEDs are individually addressable. The projector assembly further comprises a rotatable actuator supporting the LED array, wherein the rotatable actuator has a rotation axis, and wherein the rotation axis and the array axis are parallel, and a set of imaging optics positioned in optical communication with the LED array for collecting light emitted by the plurality of LEDs and forming one or more images of the LED array at a distance, wherein the one or more images include a first axis corresponding to the array axis and a second axis orthogonal to the rotation axis. Optionally, the output amplitude of the plurality of LEDs can be independently controllable.

Optionally, the set of imaging optics may further comprise one or more electro-optic elements for controlling a phase of light emitted by the plurality of LEDs. The set of imaging optics may further comprise one or more elements for retaining directional information for light emitted by the plurality of LEDs. Optionally, the rotatable actuator can control a direction of light generated by the LED array.

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