Patent Description:
<CIT> discloses a waveguide based device comprising gratings in which interference fringes corresponding to N kinds of wavelength bands are multiplexed and recorded in the same layer.

A device according to the invention is defined in appended claim <NUM>, a corresponding method in claim <NUM>. This disclosure relates to an output coupler for an optical waveguide; more specifically, and without limitation, to a Bragg grating used as an output coupler for a waveguide in a lens used for augmented reality (AR). Some systems proposed for AR use different output couplers for different wavelengths of light for an AR display. For example, an AR display could have three waveguides and three corresponding surface-relief output couplers; one for red, one for green, and one for blue. Instead of using surface-relief gratings, this disclosure describes systems and/or methods for using Bragg gratings. One possible reason for using Bragg gratings is to reduce a number of waveguides and/or output couplers in an AR display. Instead of three waveguides and three output couplers for three different colors, one waveguide and one output coupler can be used to display three different colors.

In some embodiments, light is coupled into a waveguide in a lens using an input coupler (e.g., an index-matched prism). The lens is part of a head-mounted display (e.g., AR glasses). The waveguide supports an angle range of input light, which input light propagates in the waveguide by total internal reflection from the input coupler to an output coupler. The output coupler includes one, two, or more super gratings. A super grating is an optical device with two or more gratings written in the optical device. Light exits the waveguide and is transmitted toward a user's eye. In some embodiments, a super grating is formed by exposing an optical device (e.g., exposing a substrate multiple times using UV light) to form multiple Bragg gratings.

Illustrative embodiments are described with reference to the following figures.

The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated may be employed without departing from the principles, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have the same reference label.

In the following description, for the purposes of explanation, specific details are set forth in order to provide a thorough understanding of certain inventive embodiments. However, it will be apparent that various embodiments may be practiced without these specific details. The figures and description are not intended to be restrictive.

<FIG> is a diagram of an embodiment of a near-eye display <NUM>. The near-eye display <NUM> presents media to a user. Examples of media presented by the near-eye display <NUM> include one or more images, video, and/or audio. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the near-eye display <NUM>, a console, or both, and presents audio data based on the audio information. The near-eye display <NUM> is generally configured to operate as a virtual reality (VR) display. In some embodiments, the near-eye display <NUM> is modified to operate as an augmented reality (AR) display and/or a mixed reality (MR) display.

The near-eye display <NUM> includes a frame <NUM> and a display <NUM>. The frame <NUM> is coupled to one or more optical elements. The display <NUM> is configured for the user to see content presented by the near-eye display <NUM>. In some embodiments, the display <NUM> comprises a waveguide display assembly for directing light from one or more images to an eye of the user.

<FIG> is an embodiment of a cross section <NUM> of the near-eye display <NUM> illustrated in <FIG>. The display <NUM> includes at least one waveguide display assembly <NUM>. An exit pupil <NUM> is a location where the eye <NUM> is positioned in an eyebox region when the user wears the near-eye display <NUM>. For purposes of illustration, <FIG> shows the cross section <NUM> associated with a single eye <NUM> and a single waveguide display assembly <NUM>, but a second waveguide display is used for a second eye of a user.

The waveguide display assembly <NUM> is configured to direct image light to an eyebox located at the exit pupil <NUM> and to the eye <NUM>. The waveguide display assembly <NUM> may be composed of one or more materials (e.g., plastic, glass, etc.) with one or more refractive indices. In some embodiments, the near-eye display <NUM> includes one or more optical elements between the waveguide display assembly <NUM> and the eye <NUM>.

In some embodiments, the waveguide display assembly <NUM> includes a stack of one or more waveguide displays including, but not restricted to, a stacked waveguide display, a varifocal waveguide display, etc. The stacked waveguide display is a polychromatic display (e.g., a red-green-blue (RGB) display) created by stacking waveguide displays whose respective monochromatic sources are of different colors. The stacked waveguide display is also a polychromatic display that can be projected on multiple planes (e.g. multi-planar colored display). In some configurations, the stacked waveguide display is a monochromatic display that can be projected on multiple planes (e.g. multi-planar monochromatic display). The varifocal waveguide display is a display that can adjust a focal position of image light emitted from the waveguide display. In alternate embodiments, the waveguide display assembly <NUM> may include the stacked waveguide display and the varifocal waveguide display.

<FIG> illustrates an isometric view of an embodiment of a waveguide display <NUM>. In some embodiments, the waveguide display <NUM> is a component (e.g., the waveguide display assembly <NUM>) of the near-eye display <NUM>. In some embodiments, the waveguide display <NUM> is part of some other near-eye display or other system that directs image light to a particular location.

The waveguide display <NUM> includes a source assembly <NUM>, an output waveguide <NUM>, and a controller <NUM>. For purposes of illustration, <FIG> shows the waveguide display <NUM> associated with a single eye <NUM>, but in some embodiments, another waveguide display separate, or partially separate, from the waveguide display <NUM> provides image light to another eye of the user.

The source assembly <NUM> generates image light <NUM>. The source assembly <NUM> generates and outputs the image light <NUM> to a coupling element <NUM> located on a first side <NUM>-<NUM> of the output waveguide <NUM>. The output waveguide <NUM> is an optical waveguide that outputs expanded image light <NUM> to an eye <NUM> of a user. The output waveguide <NUM> receives the image light <NUM> at one or more coupling elements <NUM> located on the first side <NUM>-<NUM> and guides received input image light <NUM> to a directing element <NUM>. In some embodiments, the coupling element <NUM> couples the image light <NUM> from the source assembly <NUM> into the output waveguide <NUM>. The coupling element <NUM> may be, e.g., a diffraction grating, a holographic grating, one or more cascaded reflectors, one or more prismatic surface elements, and/or an array of holographic reflectors.

The directing element <NUM> redirects the received input image light <NUM> to the decoupling element <NUM> such that the received input image light <NUM> is decoupled out of the output waveguide <NUM> via the decoupling element <NUM>. The directing element <NUM> is part of, or affixed to, the first side <NUM>-<NUM> of the output waveguide <NUM>. The decoupling element <NUM> is part of, or affixed to, the second side <NUM>-<NUM> of the output waveguide <NUM>, such that the directing element <NUM> is opposed to the decoupling element <NUM>. The directing element <NUM> and/or the decoupling element <NUM> may be, e.g., a diffraction grating, a holographic grating, one or more cascaded reflectors, one or more prismatic surface elements, and/or an array of holographic reflectors.

The second side <NUM>-<NUM> represents a plane along an x-dimension and a y-dimension. The output waveguide <NUM> may be composed of one or more materials that facilitate total internal reflection of the image light <NUM>. The output waveguide <NUM> may be composed of e.g., silicon, plastic, glass, and/or polymers. The output waveguide <NUM> has a relatively small form factor. For example, the output waveguide <NUM> may be approximately <NUM> wide along x-dimension, <NUM> long along y-dimension and <NUM>-<NUM> thick along a z-dimension.

The controller <NUM> controls scanning operations of the source assembly <NUM>. The controller <NUM> determines scanning instructions for the source assembly <NUM>. In some embodiments, the output waveguide <NUM> outputs expanded image light <NUM> to the user's eye <NUM> with a large field of view (FOV). For example, the expanded image light <NUM> provided to the user's eye <NUM> with a diagonal FOV (in x and y) of <NUM> degrees and or greater and/or <NUM> degrees and/or less. The output waveguide <NUM> is configured to provide an eyebox with a length of <NUM> or greater and/or equal to or less than <NUM>; and/or a width of <NUM> or greater and/or equal to or less than <NUM>.

<FIG> illustrates an embodiment of a cross section <NUM> of the waveguide display <NUM>. The cross section <NUM> includes the source assembly <NUM> and the output waveguide <NUM>. The source assembly <NUM> generates image light <NUM> in accordance with scanning instructions from the controller <NUM>. The source assembly <NUM> includes a source <NUM> and an optics system <NUM>. The source <NUM> is a light source that generates coherent or partially coherent light. The source <NUM> may be, e.g., a laser diode, a vertical cavity surface emitting laser, and/or a light emitting diode.

The optics system <NUM> includes one or more optical components that condition the light from the source <NUM>. Conditioning light from the source <NUM> may include, e.g., expanding, collimating, and/or adjusting orientation in accordance with instructions from the controller <NUM>. The one or more optical components may include one or more lens, liquid lens, mirror, aperture, and/or grating. In some embodiments, the optics system <NUM> includes a liquid lens with a plurality of electrodes that allows scanning a beam of light with a threshold value of scanning angle to shift the beam of light to a region outside the liquid lens. Light emitted from the optics system <NUM> (and also the source assembly <NUM>) is referred to as image light <NUM>.

The output waveguide <NUM> receives the image light <NUM>. The coupling element <NUM> couples the image light <NUM> from the source assembly <NUM> into the output waveguide <NUM>. In embodiments where the coupling element <NUM> is diffraction grating, a pitch of the diffraction grating is chosen such that total internal reflection occurs in the output waveguide <NUM>, and the image light <NUM> propagates internally in the output waveguide <NUM> (e.g., by total internal reflection), toward the decoupling element <NUM>.

The directing element <NUM> redirects the image light <NUM> toward the decoupling element <NUM> for decoupling from the output waveguide <NUM>. In embodiments where the directing element <NUM> is a diffraction grating, the pitch of the diffraction grating is chosen to cause incident image light <NUM> to exit the output waveguide <NUM> at angle(s) of inclination relative to a surface of the decoupling element <NUM>.

In some embodiments, the directing element <NUM> and/or the decoupling element <NUM> are structurally similar. The expanded image light <NUM> exiting the output waveguide <NUM> is expanded along one or more dimensions (e.g., may be elongated along x-dimension). In some embodiments, the waveguide display <NUM> includes a plurality of source assemblies <NUM><NUM> and a plurality of output waveguides <NUM>. Each of the source assemblies <NUM> emits a monochromatic image light of a specific band of wavelength corresponding to a primary color (e.g., red, green, or blue). Each of the output waveguides <NUM> may be stacked together with a distance of separation to output an expanded image light <NUM> that is multi-colored.

<FIG> is a block diagram of an embodiment of a system <NUM> including the near-eye display <NUM>. The system <NUM> comprises the near-eye display <NUM>, an imaging device <NUM>, and an input/output interface <NUM> that are each coupled to a console <NUM><NUM>.

The near-eye display <NUM> is a display that presents media to a user. Examples of media presented by the near-eye display <NUM> include one or more images, video, and/or audio. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the near-eye display <NUM> and/or the console <NUM> and presents audio data based on the audio information to a user. In some embodiments, the near-eye display <NUM> may also act as an AR eyewear glass. In some embodiments, the near-eye display <NUM> augments views of a physical, real-world environment, with computer-generated elements (e.g., images, video, sound, etc.).

The near-eye display <NUM> includes a waveguide display assembly <NUM>, one or more position sensors <NUM>, and/or an inertial measurement unit (IMU) <NUM>. The waveguide display assembly <NUM> includes the source assembly <NUM>, the output waveguide <NUM>, and the controller <NUM>.

The IMU <NUM> is an electronic device that generates fast calibration data indicating an estimated position of the near-eye display <NUM> relative to an initial position of the near-eye display <NUM> based on measurement signals received from one or more of the position sensors <NUM>.

The imaging device <NUM> generates slow calibration data in accordance with calibration parameters received from the console <NUM>. The imaging device <NUM> may include one or more cameras and/or one or more video cameras.

The input/output interface <NUM> is a device that allows a user to send action requests to the console <NUM>. An action request is a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application.

The console <NUM> provides media to the near-eye display <NUM> for presentation to the user in accordance with information received from one or more of the imaging device <NUM>, the near-eye display <NUM>, and the input/output interface <NUM>. In the example shown in <FIG>, the console <NUM> includes an application store <NUM>, a tracking module <NUM>, and an engine <NUM>.

The application store <NUM> stores one or more applications for execution by the console <NUM>. An application is a group of instructions, that when executed by a processor, generates content for presentation to the user. Examples of applications include: gaming applications, conferencing applications, video playback application, or other suitable applications.

The tracking module <NUM> calibrates the system <NUM> using one or more calibration parameters and may adjust one or more calibration parameters to reduce error in determination of the position of the near-eye display <NUM>.

The tracking module <NUM> tracks movements of the near-eye display <NUM> using slow calibration information from the imaging device <NUM>. The tracking module <NUM> also determines positions of a reference point of the near-eye display <NUM> using position information from the fast calibration information.

The engine <NUM> executes applications within the system <NUM> and receives position information, acceleration information, velocity information, and/or predicted future positions of the near-eye display <NUM> from the tracking module <NUM>. In some embodiments, information received by the engine <NUM> may be used for producing a signal (e.g., display instructions) to the waveguide display assembly <NUM> that determines a type of content presented to the user.

<FIG> is a simplified front view of an embodiment of a device <NUM> having a waveguide <NUM>, an input element <NUM>, and an output element <NUM>. The device <NUM> is part of a waveguide display assembly <NUM>, which is part of a display <NUM> for an artificial-reality headset (e.g., display <NUM> mounted in frame <NUM> for a near-eye display <NUM>). The waveguide <NUM> is configured to guide light from the input element <NUM> to the output element <NUM>. In some embodiments, the waveguide <NUM> is an output waveguide <NUM>. The input element <NUM> is configured to couple light from a source (e.g., from a source assembly <NUM>) into the waveguide <NUM>. The output element <NUM> is configured to out couple light from the waveguide <NUM> to an eyebox <NUM>. While a user is wearing the artificial-reality headset, the eyebox <NUM> is configured to be positioned at an eye <NUM> of the user. In some embodiments, the input element <NUM> is similar to the coupling element <NUM>. In some embodiments, the input element <NUM> comprises a prism and/or the output element <NUM> is a holographic grating.

<FIG> is a simplified side view of an embodiment of the device <NUM>. The output element <NUM> comprises one grating layer <NUM>. In some embodiments, the output element <NUM> comprises only one grating layer (e.g., instead of both a directing element <NUM> and a decoupling element <NUM>). Two different super gratings are written in the grating layer <NUM> using multiple exposures. With multiplexed exposures, the waveguide <NUM> can decouple light, such as light of three bandwidths, Red-Green-Blue (RGB), wherein each bandwidth of light source is <NUM> +/-<NUM>% (e.g., at full width, half max) from field of view angles within the waveguide (e.g., angles <NUM>-<NUM> degrees), while providing small size and low weight. See-through quality can be good because Bragg conditions are for a display-light path (e.g. angularly selective for a display-light path) which will be different for see-through light.

The input element <NUM> is a prism for coupling light into the waveguide <NUM>. Coupling through a prismatic element can be very efficient (e.g., transmission > <NUM>%) compared to using a grating element. The prism is index matched to the waveguide <NUM>. In some embodiments the input element <NUM> is an angled side of the waveguide <NUM> (e.g., the waveguide <NUM> is cut to accommodate a larger beam) (not shown) and/or a grating.

Deflection and decoupling of light by the grating layer <NUM> is diffraction caused by the super gratings. In some examples, the decoupled light may be from first order diffractions. The super gratings are Bragg gratings. Bragg gratings can be formed in many ways. In some embodiments, a grating is formed using one or more of the following: exposing material (e.g., a portion of the cladding and/or core of the waveguide <NUM>) to electro-magnetic radiation (e.g., ultra-violet (UV) light); stacking materials having different refractive indices (e.g., thin films), using resins having different refractive indices, using ion-implantation to change refractive index of a material, and/or exposing material to a thermal gradient. The waveguide <NUM> is partially exposed in a transverse direction of the waveguide, so that the Bragg grating does not extend across an entire core of the waveguide <NUM>. A transverse width w of the waveguide <NUM> is measured from a first side <NUM> of the waveguide <NUM> to a second side <NUM> of the waveguide <NUM>. The grating layer <NUM> has a depth d measured from the first side <NUM> toward the second side <NUM>. Depth d is equal to or greater than <NUM>%, <NUM>%, or <NUM>% of width w and equal to or less than <NUM>%, <NUM>%, <NUM>% or <NUM>% of width w. In some embodiments, super gratings (discussed below) are formed on the same side of the waveguide <NUM> (e.g., on the first side <NUM>). In some embodiments a first super grating is formed near one side (e.g., the first side <NUM>) of the waveguide <NUM> and a second super grating is formed near another side (e.g., the second side <NUM>) of the waveguide <NUM>. In some embodiments, the grating layer <NUM> is added to the waveguide <NUM> (e.g., formed in a material layer outside the waveguide <NUM> and then bonded to the first side <NUM> of the waveguide <NUM>).

In the embodiment shown, light diffracts from the grating <NUM> at a first bounce <NUM>-<NUM>, at a second bounce <NUM>-<NUM>, and at a third bounce <NUM>-<NUM>. Light is coupled out of the waveguide at the second bounce <NUM>-<NUM> (e.g., some light at the first bounce <NUM>-<NUM> being deflected for decoupling on the second bounce <NUM>-<NUM>), the third bounce <NUM>-<NUM> (e.g., some light at the second bounce <NUM>-<NUM> being deflected for decoupling on the third bounce <NUM>-<NUM>), and so on.

The output element <NUM> comprises a holographic Bragg grating. Holographic Bragg gratings are discussed in <CIT>, titled "Volume Bragg Grating for Waveguide Display". The output element <NUM> is formed by multiple exposures to form two super gratings that: (<NUM>) deflect light coupled by the input element <NUM>; and (<NUM>) decouple light that is deflected. In some embodiments, deflection and/or decoupling is first order diffraction.

<FIG> is a simplified drawing of an example f a first grating <NUM>-<NUM> not according to the claimed invention. The first grating <NUM>-<NUM> is a Bragg grating. A Bragg grating has alternating regions of lower refractive index and higher refractive index. The first grating <NUM>-<NUM> is periodic, defined by a pitch p-<NUM>. The pitch is from the grating equation: p*sin(θm - θi) = m*λ, where p is the pitch (also known as the grating constant), θm is the diffracted angle, θi is the incident angle, m is the order, and λ is the wavelength of diffracted light. The first grating <NUM>-<NUM> is defined by a first grating vector <NUM>-<NUM>, which has an orientation in a direction of change of light direction (e.g., slant), which the grating <NUM>-<NUM> imparts to an incident light beam, and a length proportional to the pitch p.

<FIG> is a simplified drawing of an example of a second grating <NUM>-<NUM> not according to the claimed invention. The second grating <NUM>-<NUM> is similar to the first grating <NUM>-<NUM> except the second grating <NUM>-<NUM> is defined by a second pitch p-<NUM>, which is longer than p-<NUM> and defined by a second grating vector <NUM>-<NUM>, which is longer than the first grating vector <NUM>-<NUM>.

<FIG> is a simplified drawing of an example of a third grating <NUM>-<NUM> not according to the claimed invention. The third grating <NUM>-<NUM> is similar to the second grating <NUM>-<NUM> except the third grating <NUM>-<NUM> is defined by a third pitch p-<NUM>, which is longer than the second pitch p-<NUM> and defined by a third grating vector <NUM>-<NUM>, which is longer than the second grating vector <NUM>-<NUM>.

<FIG> is a simplified drawing of an example of a super grating <NUM> not according to the claimed invention. The super grating <NUM> is a combination of gratings <NUM> that have grating vectors <NUM> oriented in a same direction. The super grating <NUM> is formed by exposing the waveguide <NUM> multiple times to UV light. The super grating <NUM> is defined by super-grating vector <NUM>. In some examples, the super grating <NUM> is a combination of n number of gratings <NUM>, wherein n is equal to or greater than <NUM>, <NUM>, <NUM>, or <NUM> and equal to or less than <NUM>, <NUM>, or <NUM> (e.g., n = <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>).

<FIG> is a simplified drawing of an example an output element <NUM>, not according to the claimed invention, having a first super grating <NUM>-<NUM> and a second super grating <NUM>-<NUM>. A first super-grating vector <NUM>-<NUM> defines the first super grating <NUM>-<NUM>. A second super-grating vector <NUM>-<NUM> defines the second super grating <NUM><NUM>-<NUM>. The first super grating <NUM>-<NUM> is offset from the second super grating <NUM>-<NUM> (e.g., the first super-grating vector <NUM>-<NUM> is skew to the second super-grating vector <NUM>-<NUM>). In some examples , both the first super grating <NUM>-<NUM> and the second super grating <NUM>-<NUM> are written in the same layer and/or written at the same time (e.g., two exposures at a time to form two Bragg gratings at a time; one Bragg grating in each super grating <NUM>). By having two super gratings that are oriented skew to one another, light of two dimensions can be out coupled by the output element <NUM> (e.g., by using two bounces from the output element <NUM>).

The first super grating <NUM>-<NUM> and the second super grating <NUM>-<NUM> can be written in the same medium (e.g., holographic medium) on one side (e.g., as opposed to surface-relief gratings written on two sides of the waveguide <NUM>). Thus, in some examples, the first super grating <NUM>-<NUM>, the second super grating <NUM>-<NUM>, and/or other super gratings <NUM> are in the same optical medium and on the same side of the optical medium. In some examples, the first super grating <NUM>-<NUM> is written on one side (e.g., the first side <NUM>) and the second super grating <NUM>-<NUM> is written on another side (e.g., the second side <NUM>), so that the first super grating <NUM>-<NUM> is separated in the z direction from the second super grating <NUM>-<NUM>.

<FIG> is an example of a solution space <NUM> for a grating <NUM>. As described in the '<NUM> application, a Bragg grating diffracts light at a certain wavelength and angle. For example, the grating <NUM>, for which the solution space <NUM> is depicted in <FIG>, diffracts green light (e.g., <NUM>) at an incoming angle of <NUM> degrees. A solution line <NUM> shows angle and wavelength combinations that one grating <NUM> diffracts.

<FIG> is an example of a solution space <NUM> for a super grating <NUM> with dense writings of gratings <NUM>. The solution space <NUM> is made up of n solution lines <NUM>, each solution line <NUM> corresponding to one grating <NUM>. <FIG> shows a first solution line <NUM>-<NUM>, a second solution line <NUM>-<NUM>, to solution line <NUM>-n.

Multiple exposures (e.g., UV exposures) are performed to create n number of gratings <NUM> with grating vectors <NUM> in the same direction but different lengths (e.g., same slant but different pitches). Exposures are done densely so that neighboring incident angles are separated by less than <NUM>, <NUM>, or <NUM> arcminutes and/or by more than <NUM> arcminute. Thus for basically all angles (e.g., between <NUM> and <NUM> degrees), there is a Bragg condition for a spectrum of light (e.g., from <NUM> to <NUM> or bands of light such as from <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>). Supported incidence cone angles include angles of light coming from the input element <NUM> as well as an angle of the in coupled light followed by deflection (e.g., first diffraction of the output element <NUM>). The output element <NUM> supports both deflection and out-coupling of a field of view (FOV) and spectrum of light. In some examples n = a number of pixels of the display +/- <NUM>%. Thus for a <NUM> pixel display, n = <NUM> +/- <NUM>%. With multiplexed exposures, one waveguide display can decouple light of the RGB spectrum (e.g., RGB bands having <NUM>-nm bandwidth, +/- <NUM> or <NUM>%) from a range of angles.

In some examples, sparse writing is used in combination with broadband light to reduce a number of gratings <NUM> in a super grating <NUM>. At a given location for a super grating <NUM><NUM> there are a first number of gratings g1 that diffract red light, a second number of gratings g2 that diffract green light, and a third number of gratings g3 that diffract blue light. In some examples, one grating can diffract red light, green light, and blue light, thus g1+g2+g3 can be less than a total number of gratings n for a super grating <NUM>. For sparse writing, g1, g2, and/or g3 are equal to or greater than <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> and equal to or less than <NUM>, <NUM>, <NUM>, or <NUM>. In some examples, the total number of gratings n for a super grating <NUM> at a given location is equal to or greater than <NUM>, <NUM>, or <NUM> and equal to or less than <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. In some examples, red light has a wavelength equal to or between <NUM> and <NUM>; green light has a wavelength equal to or between <NUM> and <NUM>; and blue light has a wavelength equal to or between <NUM> and <NUM>.

Decoupling efficiency of a super grating <NUM> can vary depending if gratings <NUM> are written sparsely or densely. For sparse writings, decoupling efficiency at a given location (e.g., at the second bounce <NUM>-<NUM> and/or at the third bounce <NUM>-<NUM>) can be equal to or greater than <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>%. Decoupling efficiency can be high because gratings at different locations out couple different wavelengths of light for a given input angle. For dense writing, decoupling efficiency can be less than <NUM>% at a given location (e.g., between <NUM>% and <NUM>%; at the second bounce <NUM>-<NUM> and/or at the third bounce <NUM>-<NUM>). In some examples, decoupling efficiency increases as light propagates through the waveguide <NUM>. Sparse gratings may be configured to have high decoupling efficiency for narrower bands (e.g. smaller than <NUM>), while dense gratings may be configured to have a changing decoupling efficiency for a broader bands (e.g. greater than <NUM>).

<FIG> is an embodiment of an output element <NUM> having a super grating <NUM> according to the claimed invention. The super grating <NUM> varies spatially. The super grating <NUM> comprises a plurality of gratings. The plurality of gratings are oriented in the same direction. Each of the plurality of gratings varies spatially so that the super grating <NUM> has different sets of pitches at different locations. In some embodiments, the super grating <NUM> is formed by superimposing a plurality of chirped gratings. The super grating <NUM> can be formed by coarse exposures. In this way, for a given incidence angle with broad spectrum of light, some wavelengths will diffract (deflect or decouple) from a first bounce at a first location and other wavelengths, which were not yet diffracted, are diffracted at a second location after a second bounce, and other sets of wavelengths are diffracted at other locations, and so on until the q-th location. Thus light in the spectrum will eventually be diffracted after a few bounces in the waveguide (e.g., q = <NUM>, <NUM>, or <NUM>). Dense exposures are thus not needed at each location (e.g., instead of <NUM>,<NUM> exposures, less than <NUM> exposures can be used at a given location). Gratings at the second location don't have the same pitches as gratings at the first location. Thus a first super-grating vector <NUM>-<NUM> at the first location is different from a second super-grating vector <NUM>-<NUM> at the second location and different from a q-th super-grating vector <NUM>-q at the q-th location. The first super-grating vector <NUM>-<NUM>, the second super-grating vector <NUM>-<NUM>, and the q-th super grating vector <NUM>-q have the same direction and different magnitudes. The first super-grating vector <NUM>-<NUM>, the second super-grating vector <NUM>-<NUM>, and the q-th super grating vector <NUM>-q have different magnitudes because pitches of the plurality of gratings vary as a function of location. A second super grating can be used with gratings oriented in a different direction to couple light out of the waveguide <NUM> in two dimensions. The second super grating can also have spatially-varying pitch.

<FIG> is an embodiment of a solution space <NUM> for a super grating <NUM> having a plurality of gratings that vary spatially. A first set <NUM>-<NUM> of solutions are shown in solid lines. A second set <NUM>-<NUM> of solutions are shown in dashed lines. The first set <NUM>-<NUM> of solutions are solution lines <NUM> for the plurality of gratings at the first location. The second set <NUM>-<NUM> of solutions are solution lines <NUM> for the plurality of gratings at the second location. The first set <NUM>-<NUM> of solutions are different than the second set <NUM>-<NUM> of solutions. In some embodiments, a third set, a fourth set, and/or a fifth set of solutions exist for a third location, a fourth location, and/or a fifth location. Applicant has determined by simulation that five locations can be sufficient to out couple a spectrum of light from <NUM> to <NUM>.

<FIG> is a simplified drawing of vector paths of light interacting with gratings <NUM> of the output element <NUM>. Light is coupled into the waveguide <NUM> by the input element <NUM>. In some examples, the input element <NUM> imparts a direction change to light as depicted by input vector <NUM> (e.g., by an input grating). Diffraction, either directing or decoupling, from a first grating is depicted by a first grating vector <NUM>-<NUM>. Diffraction, either directing or decoupling, from a second grating is depicted by a second grating vector <NUM>-<NUM>. After light is changed direction by the input element <NUM>, diffracted by the first grating, and diffracted by the second grating after the first grating, the light has a direction (e.g., k vector or wave vector) similar to a direction of light entering into the input element <NUM> (see vectors on a left side of the figure). Light that is changed direction by the input element <NUM>, diffracted by the second grating, and diffracted by the first grating after being diffracted by the second grating also has a direction (e.g., k vector or wave vector) similar to light entering the input element <NUM> (see vectors on a right side of the figure). The first grating vector <NUM>-<NUM> and the second grating vector <NUM>-<NUM> sum to zero when projected onto axis <NUM>.

In some examples, the input element <NUM> doesn't change direction of light; light is input at a calculated offset angle (e.g., input at offset input <NUM>), so that light will diffract out of the waveguide in a direction as if the input element <NUM> had changed direction of the light by an amount of the input vector <NUM>. In some examples, a combination of an offset angle and using the input element <NUM> to change the direction of light is equivalent to changing light by an amount equal to the input vector <NUM>. In some examples, light is coupled into a waveguide (e.g., waveguide <NUM>) at a known offset angle (e.g., because waveguides are canted) and grating vectors <NUM> are calculated so that input angle is different than output angle.

<FIG> an example of a flowchart of a process <NUM> for fabricating an output element, not according to the claimed invention. Process <NUM> begins in step <NUM> with obtaining a waveguide (e.g., waveguide <NUM>). In step <NUM> a first Bragg grating (e.g., a grating of the first super grating <NUM>-<NUM>) is created (e.g., by UV exposure to a grating layer). The first Bragg grating has a first orientation (e.g., orientation of the first super-grating vector <NUM>-<NUM>). In step <NUM> a second Bragg grating (e.g., a grating of the second super grating <NUM>-<NUM>) is created (e.g., by UV exposure to the grating layer). The second Bragg grating has a second orientation (e.g., orientation of the second super-grating vector <NUM>-<NUM>). The first Bragg grating and the second Bragg grating are part of the output element <NUM>. The first super grating spatially overlaps with the second super grating. In some examples, the first super grating is spatially separate from the second super grating.

Embodiments of the invention may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

The foregoing description of the embodiments of the disclosure has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

Some portions of this description describe the embodiments of the disclosure in terms of algorithms and symbolic representations of operations on information. These algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art. These operations, while described functionally, computationally, or logically, are understood to be implemented by computer programs or equivalent electrical circuits, microcode, or the like. Furthermore, it has also proven convenient at times, to refer to these arrangements of operations as modules, without loss of generality. The described operations and their associated modules may be embodied in software, firmware, and/or hardware.

Steps, operations, or processes described may be performed or implemented with one or more hardware or software modules, alone or in combination with other devices. In some embodiments, a software module is implemented with a computer program product comprising a computer-readable medium containing computer program code, which can be executed by a computer processor for performing any or all of the steps, operations, or processes described.

Claim 1:
A device comprising:
a waveguide (<NUM>); and
a super grating (<NUM>), wherein:
the super grating comprises a plurality of gratings;
the plurality of gratings are configured to couple light out of the waveguide; and
the super grating varies spatially so that the super grating has a first set of pitches at a first location and a second set of pitches at a second location to out couple some wavelengths of light for a given input angle from the waveguide at the first location and out couple other wavelengths of light for the given input angle from the waveguide at the second location.