Patent Description:
The present disclosure relates to wearable headsets, and in particular to components and modules for wearable visual display headsets.

Head mounted displays (HMD), helmet mounted displays, near-eye displays (NED), and the like are being used increasingly for displaying virtual reality (VR) content, augmented reality (AR) content, mixed reality (MR) content, etc. Such displays are finding applications in diverse fields including entertainment, education, training and biomedical science, to name just a few examples. The displayed VR / AR / MR content can be three-dimensional (3D) to enhance the experience and to match virtual objects to real objects observed by the user. Eye position and gaze direction, and/or orientation of the user may be tracked in real time, and the displayed imagery may be dynamically adjusted depending on the user's head orientation and gaze direction, to provide a better experience of immersion into a simulated or augmented environment.

Compact display devices are desired for head-mounted displays. Because a display of HMD or NED is usually worn on the head of a user, a large, bulky, unbalanced, and/or heavy display device would be cumbersome and may be uncomfortable for the user to wear.

Projector-based displays provide images in angular domain, which can be observed by a user's eye directly, without an intermediate screen or a display panel. A pupil replication waveguide is used to carry the image in angular domain to the user's eye. The lack of a screen or a display panel in a scanning projector display enables size and weight reduction of the display.

Ideally, pupil replication waveguides provide a sufficient directivity to make sure that the images being displayed may only be seen by the wearer of the display and not by outside observers. In many current pupil replication waveguides however, a small but noticeable portion of display light leaks out of the display, enabling outside observers to see some of the displayed imagery and impeding an eye contact with the wearer of the display.

<CIT> describes an apparatus for displaying an image comprising: a first optical substrate comprising at least one waveguide layer configured to propagate light in a first direction, wherein the at least one waveguide layer of the first optical substrate comprises at least one grating lamina configured to extract the light from the first substrate along the first direction; and a second optical substrate comprising at least one waveguide layer configured to propagate the light in a second direction, wherein the at least one waveguide layer of the second optical substrate comprises at least one grating lamina configured to extract light from the second substrate along the second direction; wherein the at least one grating lamina of at least one of the first and second optical substrates comprises an SBG in a passive mode.

<CIT> describes mastering systems and methods of fabricating waveguides and waveguide devices using such mastering. Mastering systems for fabricating holographic waveguides can include using a master to control the application of energy (e.g. a laser, light, or magnetic beam) onto a liquid crystal substrate to fabricate a holographic waveguide into the liquid crystal substrate. Mastering systems for fabricating holographic waveguides can include a variety of features. These features include, but are not limited to: chirp for single input beam copy (near i.e. hybrid contact copy), dual chirped gratings (for input and output), zero order grating for transmittance control, alignment reference gratings, <NUM>:<NUM> construction, position adjustment tooling to enable rapid alignment, optimization of lens and window thickness for multiple RKVs simultaneously, and avoidance of other orders and crossover of the diffraction beam.

In accordance with an aspect, there is provided a pupil replication waveguide according to claim <NUM>.

In some embodiments, the diffraction grating comprises a stack of first, second, and third grating layers, the second grating layer being disposed between the first and third grating layers and the fringes extending across the stack. A refractive index contrast of the diffraction grating in each one of the first, second, and third layers is constant, and the refractive index contrast of the second grating layer is higher than the refractive index contrast of the first and third grating layers. Thicknesses of the first and third grating layers may be substantially equal to each other. In some embodiments, the thicknesses of the first, second, and third grating layers are substantially equal to each other, and the refractive index contrast of the second grating layer are higher than the refractive index contrast of the first and third grating layers.

In some embodiments, the values of the refractive index contrast of the first and third grating layers are substantially equal to each other. A thickness of the second grating layer may be equal to or greater than each one of the thickness of the first and third grating layers. The thickness of the second grating layer may be equal to or greater than a sum of thicknesses of the first and third grating layers.

In some embodiments, a refractive index of the fringes is substantially the same in the first, the second, and the third grating layers, and a refractive index of the substrate of the second grating layer is different from a refractive index of the substrate of the first and third grating layers. In some embodiments, a refractive index of the substrate is substantially the same in the first, the second, and the third grating layers, and a refractive index of the fringes in the second grating layer is different from a refractive index of the fringes in the first and third grating layers. A diffraction efficiency of diffracting the display light into the non-blazed diffraction order may be less than <NUM>%.

In some embodiments, the diffraction grating is a Bragg grating. A refractive index profile of the Bragg grating in a direction perpendicular to the fringes may be e.g. sinusoidal. For any type of the diffraction grating, the refractive index contrast profile may be a smoothly varying function, e.g. a Gaussian function. An input grating may be provided for in-coupling the display light into the slab.

In accordance with another aspect, there is provided a method of manufacturing a pupil replication waveguide according to claim <NUM>.

In some embodiments, the first, second, and third substrate layers are formed by at least one of a spin-on, an inkjet, or a flowable deposition process. The plurality of slanted fringes may be formed by at least one of atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), or physical vapor deposition (PVD).

In accordance with a further aspect, there is further provided a method of manufacturing a pupil replication waveguide according to claim <NUM>.

Exemplary embodiments will now be described in conjunction with the drawings, in which:.

While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof.

As used herein, the terms "first", "second", and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated.

Light leaking outside of a near-eye display based on a projector and a pupil replication waveguide may be caused by diffraction of display light at a diffraction grating of the pupil replication waveguide in an undesired direction, i.e. outside of the display towards outside world, and not inside of the display towards the user's eyes. For blazed diffraction gratings, i.e. gratings with grooves or fringes slanted to diffract the impinging light more efficiently into one diffraction order, e.g. first diffraction order, than into an opposite diffraction order, e.g. minus first diffraction order, some light may still leak in the direction of the non-blazed diffraction order, that is, outside of the display. The leaked display light may be distracting to people interacting with the wearer of the near-eye display, and may enable the other viewers to see the displayed content (text, images, etc.), potentially causing privacy issues.

In accordance with the present disclosure, a diffraction grating of a pupil replication waveguide may be configured to reduce diffraction in unwanted direction(s), i.e. into non-blazed orders of diffraction. To that end, a refractive index contrast profile of a diffraction grating in a direction of thickness of the diffraction grating, that is, across the thickness of the diffraction grating, may be reduced at extremities of the diffraction grating, that is, at top and bottom surfaces of the diffraction grating, as compared to the refractive index contrast at the middle thickness of the diffraction grating. Such apodization of the refractive index contrast can suppress the diffraction of light into the unwanted or non-blazed orders of diffraction. Herein, the refractive index contrast is defined as a difference of refractive index of the diffraction grating fringes and the refractive index of the underlying substrate in which the fringes are suspended.

The refractive index contrast apodization may be achieved by a variety of means. In some embodiments, the diffraction grating may be layered, each layer having its own refractive index contrast. In some embodiments, a more smooth variation may be produced by processing, i.e. controlled baking, of the diffraction grating layer materials. In some embodiments, a duty cycle, or a fill factor, of a diffraction grating may be varied in going through the thickness of the diffraction grating by tapering or otherwise shaping diffraction grating grooves or fringes. These and other embodiments will be considered in more detail further below.

Referring to <FIG>, a pupil replication waveguide <NUM> includes a slab <NUM> of a transparent material for propagating display light <NUM> in the slab <NUM> by sequential total internal reflections (TIR) from top and bottom parallel surfaces of the slab <NUM>. Herein, the term "transparent" includes both completely transparent, as well as partially transparent or translucent, i.e. somewhat absorbing or scattering, but transparent enough for a sufficient amount of display light to be conveyed to the user's eye for the user to see the displayed image. The slab <NUM> is generally plano-parallel, although slight curvature of the slab may be acceptable in some cases.

A diffraction grating <NUM> is supported by the slab <NUM>. The diffraction grating <NUM> includes a plurality of fringes <NUM> in a substrate <NUM>. A refractive index of the fringes <NUM> is different from a refractive index of the substrate <NUM>. The refractive index of the fringes <NUM> may be larger or smaller than the refractive index of the substrate <NUM>. A refractive index contrast is defined herein as a modulus of difference between the refractive indices of the fringes <NUM> and the substrate <NUM>. The fringes <NUM> are slanted as shown in <FIG> for out-coupling a greater portion <NUM> of the display light <NUM> from the slab <NUM> for observation of the display light <NUM> by a user's eye <NUM>. Typically, the greater portion <NUM> is about <NUM>% to <NUM>% of the display light <NUM> in optical power levels. A smaller portion <NUM> of the display light <NUM> is out-coupled in a "wrong" direction, i.e. outside of the near-eye display, and may be observed by others. As explained above, it is desirable to reduce the smaller portion <NUM>. In some embodiments, the smaller portion <NUM> may be reduced to at least <NUM>% of the optical power level of the display light <NUM>. An input coupler, such as an input diffraction grating, may be provided in the pupil replication waveguide <NUM> for in-coupling the display light <NUM> into the slab <NUM>.

Referring to <FIG>, diffraction of the display light <NUM> on the diffraction grating <NUM> is shown in more detail. The fringes <NUM> of the diffraction grating <NUM> are tilted, or slanted, towards the impinging display light <NUM> to diffract the greater portion <NUM> of the display light <NUM> into a blazed diffraction order <NUM>. The smaller portion <NUM> of the display light <NUM> is diffracted into a non-blazed diffraction order <NUM>.

Referring to <FIG>, a relative permittivity ε of a diffraction grating <NUM> for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, is plotted against x- and z-coordinates in micrometers. The x-coordinate is a lateral coordinate along a surface of the diffraction grating <NUM>, and the z-coordinate is a thickness coordinate, i.e. a coordinate in a direction of thickness <NUM> of the diffraction grating <NUM>, of a particular location within diffraction grating <NUM>. The diffraction grating <NUM> includes a plurality of slanted fringes <NUM> of high permittivity, which is equal to <NUM> in this example, suspended in a substrate material <NUM> of low permittivity of <NUM>. Herein, the terms "high" and "low" are relative to one another, i.e. the fringe permittivity is higher than the substrate permittivity. In some embodiments, the fringe <NUM> permittivity is lower than the substrate <NUM> permittivity. For non-magnetic, non-absorbing media, the relative permittivity εr and the refractive index n are related as εr = n<NUM>. Accordingly, the slanted fringes <NUM> have the index of refraction nF =<NUM>, and the substrate material <NUM> has the index of refraction nS=<NUM>. The refractive index contrast Δn = |nF - nS| is equal to <NUM> in this case. The slanted fringes <NUM> may be formed lithographically on a transparent slab, not shown, and the substrate material <NUM> may be coated onto the slanted fringes <NUM> by spin-coating, for example.

<FIG> shows a result of computation of the blazed diffraction order diffraction efficiency <NUM> vs. angle of incidence for the diffraction grating <NUM> of <FIG>. Vertical lines <NUM> denote an angular range within which the display light is guided by the waveguide slab (not shown) supporting the diffraction grating <NUM>. In this example, the blazed diffraction order diffraction efficiency <NUM> reaches about <NUM>%. In comparison, a computed non-blazed diffraction order diffraction efficiency <NUM>, shown in <FIG>, reaches only about <NUM>% (the vertical scales in <FIG> are different). Even though this does not seem much as compared to the blazed diffraction order diffraction efficiency <NUM>, the <NUM>% of incoming display light may become quite noticeable to outside observers of a near-eye display with this waveguide, and may appear distracting or annoying to the outside observers, and may impede or even completely prevent the eye contact with the display wearer.

Referring now to <FIG>, a relative permittivity of a diffraction grating <NUM> for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, is plotted against x- and z-coordinates in micrometers. The x-coordinate is a lateral coordinate, and the z-coordinate is a thickness coordinate of a particular location within the diffraction grating <NUM>. As shown in <FIG>, the diffraction grating <NUM> includes a stack of first <NUM>, second <NUM>, and third <NUM> grating layers. The second grating layer <NUM> is disposed in the middle, i.e. between the first <NUM> and third <NUM> grating layers. The first <NUM> and third <NUM> grating layers have substantially a same thickness. Herein and throughout the rest of the specification, the term "substantially" when applied to a parameter means within <NUM>% of a median value of the parameter, for certainty.

The second grating layer <NUM> is thicker than any of the first <NUM> and third <NUM> grating layers, specifically about <NUM> times thicker in this example. In other words, the thickness of the second grating layer <NUM> is substantially equal to a sum thickness of the first <NUM> and third <NUM> grating layers. For example, in some embodiments, the thickness of the first <NUM> and third <NUM> grating layer may be between <NUM> and <NUM>, and the thickness of the second grating layer <NUM> may be between <NUM> and <NUM>.

A plurality of slanted fringes <NUM> extend through the first <NUM>, second <NUM>, and third <NUM> grating layers. The relative permittivity of the slanted fringes <NUM> may vary from layer to layer. The slanted fringes <NUM> are suspended in a substrate material <NUM> having a relative permittivity that also varies from layer to layer, and is lower than the relative permittivity of the fringes <NUM>. The refractive index of the substrate material <NUM> is lower than the refractive index of the fringes <NUM>, for each layer <NUM>, <NUM>, and <NUM> of the diffraction grating <NUM>.

The fringes <NUM> of the diffraction grating <NUM> have the refractive index nF of <NUM> in the first <NUM> and third <NUM> grating layers, and the refractive index nF of <NUM> in the second grating layer <NUM>. The substrate material <NUM> has the refractive index nS of <NUM> in the first <NUM> and third <NUM> grating layers, and the refractive index nS of <NUM> in the second grating layer <NUM>. Consequently, the refractive index contrast Δn = |nF - nS| of each one of the first <NUM>, second <NUM>, and third <NUM> grating layers, while being constant across each grating layer <NUM>, <NUM>, <NUM>, varies from layer to layer: the index contrast Δn is equal to <NUM> for the first <NUM> and third <NUM> grating layers, and is equal to <NUM> for the second grating layer <NUM>, i.e. the refractive index contrast of the second grating layer <NUM> is higher than the refractive index contrast of the first <NUM> and third <NUM> grating layers. The refractive index contrast profile of the diffraction grating <NUM> along a thickness direction <NUM>, i.e. z-axis, of the diffraction grating <NUM> is symmetrical, such that the refractive index contrast Δn is larger at a middle than at both sides of the refractive index contrast profile. It is noted that the refractive index values used herein are meant only as examples; the refractive index values and the refractive index contrast values may differ depending on the materials used. It is also to be understood that the statement of a refractive index value for examples considered herein implies a certain tolerance range, e.g. the refractive index of <NUM> means a range from <NUM> to <NUM>, the refractive index of <NUM> means a range from <NUM> to <NUM>, and so forth.

Referring to <FIG>, a computed diffraction efficiency <NUM> for a blazed diffraction order reaches about <NUM>%, which is slightly above one half of the blazed diffraction order diffraction efficiency <NUM> (<FIG>) of the diffraction grating <NUM> of <FIG>, which is used as a reference. The lower value of maximum diffraction efficiency as compared to that of <FIG> may be caused by a lower overall refractive index contrast Δn, due to the fact that only the middle, second layer <NUM> has the higher refractive index contrast Δn of <NUM>, and the remaining first <NUM> and third <NUM> layers have the lower refractive index contrast Δn of <NUM>. Notably, the maximum diffraction efficiency <NUM> into the non-blazed diffraction order is reduced much more dramatically, to below <NUM>%, i.e. by about <NUM> times, within the angular range of the waveguide <NUM> outlined with the boundary lines <NUM> (<FIG>) denoting an angular range for TIR-guided light. Thus, the apodization of the z-profile of the refractive index contrast Δn of the diffraction grating <NUM> of <FIG> lessens the portion of the display light out-coupled into the non-blazed diffraction order <NUM> (<FIG>), to a higher degree than the refractive index contrast of the blazed portion <NUM>. Herein and throughput the specification, the term "apodization" in reference to the refractive index contrast means reduction of the refractive index contrast at the top and bottom surfaces of the diffraction grating <NUM>, so as to smooth out the transition to zero refractive index contrast outside of the diffraction grating <NUM>, i.e. above or below the diffraction grating <NUM> as viewed in <FIG>.

Turning to <FIG>, a relative permittivity of a diffraction grating <NUM> for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, is plotted against x- and z-coordinates in micrometers. The diffraction grating <NUM> includes a stack of first <NUM>, second <NUM>, and third <NUM> grating layers. The second grating layer <NUM> is disposed in the middle, i.e. between the first <NUM> and second <NUM> grating layers. The first <NUM> and third <NUM> grating layers have substantially a same thickness, and the second grating layer <NUM> is thicker, e.g. twice as thick as each one of the first <NUM> and third <NUM> grating layers. By way of a non-limiting example, the thickness of the first <NUM> and third <NUM> grating layer may be between <NUM> and <NUM>, and the thickness of the second grating layer <NUM> may be between <NUM> and <NUM>.

A plurality of slanted fringes <NUM> extend through the first <NUM>, second <NUM>, and third <NUM> grating layers. The relative permittivity εF and, accordingly, the refractive index nF of the slanted fringes <NUM> varies from layer to layer, and is greater in the second grating layer <NUM>. The fringes <NUM> are suspended in, or supported by, a substrate <NUM>. The refractive index nS of the substrate <NUM> is at the same constant value of <NUM> for the first <NUM>, the second <NUM>, and the third <NUM> grating layers. Since the refractive index nF of the substrate <NUM> within the second grating layer <NUM> is different from the refractive index of the fringes within the first <NUM> and third <NUM> grating layers, the refractive index contrast Δn = |nF - nS| of each one of the first <NUM>, second <NUM>, and third <NUM> grating layers, while being constant across each grating layer, varies from layer to layer: the index contrast Δn is equal to <NUM> for the first <NUM> and third <NUM> grating layers, and is equal to <NUM> for the second grating layer <NUM>. The refractive index contrast profile of the diffraction grating <NUM> along a thickness direction <NUM>, i.e. z-axis, of the diffraction grating is approximately symmetrical, such that the refractive index contrast Δn is larger at a middle than at both sides of the refractive index contrast profile. It is noted that, while the diffraction grating <NUM> of <FIG> is structurally different from the diffraction grating <NUM> of <FIG>, the refractive index contrast profile of these two gratings is substantially the same.

<FIG> shows a computed diffraction efficiency <NUM> for display light diffracted by the diffraction grating <NUM> of <FIG> into a blazed diffraction order. The maximum diffraction efficiency is about <NUM>%, which is about one half of the blazed diffraction order diffraction efficiency <NUM> of the diffraction grating <NUM> of <FIG> used herein as a reference. <FIG> illustrates a computed diffraction efficiency <NUM> for the display light diffracted into a non-blazed diffraction order. The maximum diffraction efficiency <NUM> for the non-blazed diffraction order is dramatically reduced, to a value below <NUM>% within the angular range of the waveguide <NUM> outlined with boundary lines <NUM> (<FIG>) denoting an angular range for guided light. Thus, the apodization of the z-profile of the refractive index contrast Δn of the diffraction grating <NUM> of <FIG> also lessens the portion of the display light out-coupled into the non-blazed diffraction order <NUM> (<FIG>), similar to the diffraction grating <NUM> of <FIG>.

Turning to <FIG>, a relative permittivity of a diffraction grating <NUM> for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, is plotted against x- and z-coordinates in micrometers. The diffraction grating <NUM> includes a stack of first <NUM>, second <NUM>, and third <NUM> grating layers. The second grating layer <NUM> is disposed in the middle, i.e. between the first <NUM> and second <NUM> grating layers. The first <NUM> and third <NUM> grating layers have substantially a same thickness, and the second grating layer <NUM> is thicker, e.g. twice as thick as each one of the first <NUM> and third <NUM> grating layers. For example, the thickness of the first <NUM> and third <NUM> grating layer may be between <NUM> and <NUM>, and the thickness of the second grating layer <NUM> may be between <NUM> and <NUM>.

A plurality of slanted fringes <NUM> extend through the first <NUM>, second <NUM>, and third <NUM> grating layers. The relative permittivity εF and, accordingly, the refractive index nF of the slanted fringes <NUM> is the same for each grating layer <NUM>, <NUM>, and <NUM>; for all three layers, the refractive index nF of the slanted fringes <NUM> is equal to <NUM> in this example.

The slanted fringes <NUM> are suspended in a substrate <NUM>. The refractive index nS of the substrate <NUM> material varies from layer to layer. In the first grating layer <NUM> and the third grating layer <NUM>, the refractive index nS of the substrate <NUM> is equal to <NUM>; and in the second grating layer <NUM>, the refractive index nS of the substrate <NUM> is lower, being equal to <NUM>. Accordingly, the refractive index contrast Δn = |nF - nS| of each one of the first <NUM>, second <NUM>, and third <NUM> grating layers varies from layer to layer: the index contrast Δn is equal to <NUM> for the first <NUM> and third <NUM> grating layers, and is equal to <NUM> for the second grating layer <NUM>. The refractive index contrast profile of the diffraction grating <NUM> along a thickness direction <NUM>, i.e. z-axis, of the diffraction grating may be made symmetrical, such that the refractive index contrast Δn is larger at a middle than at both sides of the refractive index contrast profile. It is noted that the refractive index contrast profile is the same as in the diffraction grating <NUM> of <FIG> and the diffraction grating <NUM> of <FIG>.

<FIG> shows a computed diffraction efficiency <NUM> for display light diffracted by the diffraction grating <NUM> of <FIG> into a blazed diffraction order. The maximum diffraction efficiency is about <NUM>%, which is over one half of the blazed diffraction order diffraction efficiency <NUM> of the diffraction grating <NUM> of <FIG> used herein as a reference. Referring to <FIG>, a maximum diffraction efficiency for the non-blazed diffraction order <NUM> is also considerably reduced, to a value below <NUM>% within the angular range of the waveguide <NUM> outlined with boundary lines <NUM> (<FIG>). Thus, the apodization of the z-profile of the refractive index contrast Δn of the diffraction grating <NUM> of <FIG> lessens the portion of the display light out-coupled into the non-blazed diffraction order <NUM> (<FIG>) to a much greater degree than the portion of display light out-coupled into the blazed diffraction order.

In the examples of the diffraction grating <NUM> of <FIG>, the diffraction grating <NUM> of <FIG>, and the diffraction grating <NUM> of <FIG>, the central (second) grating layer is twice as thick as the outer grating layers (first and third), and the refractive index contrast of the central grating layer is twice higher. Other configurations are possible for the above diffraction gratings. By way of a non-limiting example, the thicknesses of all three grating layers may be made substantially equal to each other, and the refractive index contrast of the central grating layer may be higher, e.g. approximately three times higher than the refractive index contrast of the outer grating layers. Furthermore, the thicknesses of the outer grating layers do not need to be the same, and the number of layers may be grater than three. In some embodiments, the layer structure is symmetrical about the central thickness of the diffraction grating; in other embodiments, it is quasi-symmetrical or even not symmetrical. Generally, the apodization may approximate a smoothly varying bell-shaped function, such as Gaussian function, for example.

Referring to <FIG>, a diffraction grating 700A for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, includes a plurality of slanted fringes 708A of high refractive index suspended in a substrate material 710A of low refractive index. Herein, the terms "high" and "low" are relative to one another, i.e. the fringe refractive index is higher than the substrate refractive index. The fringes 708A have a refractive index that smoothly varies in a thickness direction <NUM>. The refractive index at a middle point <NUM> of the thickness is higher than at top and bottom surfaces of the diffraction grating 700A. By way of a non-limiting example, the maximum refractive index of the fringes 708A at the middle point <NUM> is <NUM>, and the refractive index at the top and bottom surfaces is <NUM>. The substrate 710A refractive index is uniform at <NUM> in this example. Accordingly, the refractive index profile of the diffraction grating 700A has a bell-like shape with the maximum of <NUM> and minimum of <NUM>. Such a configuration provides a smooth apodization of the refraction index contrast profile, which may considerably reduce the portion of the display light out-coupled into the undesired, non-blazed diffraction order.

Referring to <FIG>, a diffraction grating 700B for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, includes a plurality of slanted fringes 708B of high refractive index suspended in a substrate material 710B of low refractive index. As in examples above, the terms "high" and "low" are relative to one another, i.e. the fringe refractive index is lower than the substrate refractive index. The fringes 708B have a constant refractive index of <NUM> in this example. Refractive index of the substrate material 710B smoothly varies in a thickness direction <NUM>. The refractive index of the substrate material 710B is lower at a middle point <NUM> of the thickness than at top and bottom surfaces of the diffraction grating 700B. The minimum refractive index at the middle point <NUM> is <NUM>, and the refractive index at the top and bottom surfaces is <NUM>. Accordingly, the refractive index profile of the diffraction grating 700B of <FIG> has a same or similar bell shape as the diffraction grating 700A of <FIG>, with the maximum of <NUM> at the middle point <NUM> and minimum of <NUM> at outer surfaces of the diffraction grating 700B.

Referring now to <FIG>, a Bragg grating <NUM> for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, includes a plurality of slanted sinusoidal fringes <NUM> of a refractive index varying from <NUM> to <NUM>. Herein, the term "sinusoidal fringes" means diffraction grating fringes that have refractive index varying along a fringe direction <NUM> perpendicular to the fringes <NUM> sinusoidally, e.g. with an amplitude of <NUM> in this example (<NUM> to <NUM>). The refractive index contrast is the same across the entire Bragg grating <NUM>.

In some embodiments, the Bragg grating <NUM> may be formed by providing a two-beam optical interference pattern in a photosensitive material, which changes its index of refraction upon illumination. Ultraviolet (UV) light may be used to form the two-beam optical interference pattern in a UV-sensitive polymer or another material. The two-beam interference pattern may be formed by directing two recording UV beams to the photosensitive substrate. The orientations of the recording beams may be selected to cause as much light as possible to diffract in a direction of an eyebox of a near-eye display. In some embodiments, a plurality of such exposures may be performed at different angles; for such cases, the resulting fringe pattern may be non-sinusoidal and/or irregularly shaped to diffract the display light with high efficiency at a plurality of angles of incidence corresponding to the plurality of exposing angles.

<FIG> shows a result of computing the blazed diffraction order diffraction efficiency <NUM> vs. angle of incidence at the diffraction grating <NUM> of <FIG>. Vertical lines <NUM> denote an angular range within which the display light is guided by the waveguide slab supporting the diffraction grating <NUM>, e.g. the slab <NUM> of the pupil replication waveguide <NUM> of <FIG>. In this example, the blazed diffraction order diffraction efficiency <NUM> of <FIG> (i.e. to the eyebox of the near-eye display) reaches about <NUM>%.

<FIG> shows a result of computing the non-blazed diffraction order diffraction efficiency <NUM> vs. angle of incidence for the diffraction grating <NUM> of <FIG>. The computed non-blazed diffraction order diffraction efficiency <NUM>, shown in <FIG>, reaches only about <NUM>%. Even though this does not seem much as compared to the blazed diffraction order diffraction efficiency <NUM>, <NUM>% of incoming display light may become quite noticeable to outside observers of a near-eye display using such a pupil replication waveguide. Thus, a non-apodized refractive index contrast may result in a significant leaking of display light outside of the near-eye display, even for cases where the refractive index variation of the diffraction grating fringes is smooth, e.g. sinusoidal.

Turning to <FIG>, a Bragg grating <NUM> for a pupil replication waveguide, e.g. the pupil replication waveguide <NUM> of <FIG>, includes a plurality of slanted sinusoidal fringes <NUM> running through a stack of first <NUM>, second <NUM>, and third <NUM> grating layers. A relative permittivity of the diffraction grating <NUM> is plotted against x- and z-coordinates in micrometers. The x-coordinate is a lateral coordinate, and the z-coordinate is a thickness coordinate of a particular location within the diffraction grating <NUM>. In other words, the z-coordinate is parallel to a thickness direction <NUM>. The second grating layer <NUM> of the diffraction grating <NUM> is disposed in the middle, i.e. between the first <NUM> and second <NUM> grating layers of the diffraction grating <NUM>. The first <NUM> and third <NUM> grating layers have a same thickness, and the second (middle) layer <NUM> is approximately twice as thick as each one of the first <NUM> and third <NUM> grating layers. In this example, the thickness of the first <NUM> and third <NUM> grating layer is between <NUM> and <NUM>, and the thickness of the second grating layer <NUM> is between <NUM> and <NUM>.

The amplitude of sinusoidal variation of the refractive index in the fringes <NUM>, i.e. the refractive index contrast, is different in different grating layers. In the example shown, the index contrast of the first <NUM> and third <NUM> grating layers is <NUM> with the refractive index spatially varying form <NUM> to <NUM>, and the index contrast of the second grating layer <NUM> is <NUM> with the refractive index spatially varying form <NUM> to <NUM>. Such a variation pattern may be obtained, for example, by stacking together the first <NUM>, second <NUM>, and third <NUM> grating layers, with the second grating layer <NUM> having a higher higher concentration of the photosensitive material than the first <NUM> and third <NUM> grating layers, and simultaneously irradiating the stack with two writing UV waves to create a writing UV interference pattern extending across all three grating layers. One may also use apodize the beam intensity to be the strongest in the middle of the grating.

Referring to <FIG>, a computed diffraction efficiency <NUM> for a blazed diffraction order reaches about <NUM>%, which is slightly lower than the blazed diffraction order diffraction efficiency <NUM> (<FIG>) of the Bragg grating <NUM> of <FIG>. The slightly lower value of maximum diffraction efficiency may be caused by a lower overall refractive index contrast Δn, due to the fact that only the middle, the second layer <NUM> has the refractive index contrast Δn of <NUM>, and the first <NUM> and third <NUM> grating layers have the lower refractive index contrast Δn of <NUM>. Notably, the maximum diffraction efficiency <NUM> for the non-blazed diffraction order is reduced much more dramatically, to below <NUM>%, i.e. at least <NUM> times, within the angular range of the waveguide <NUM> outlined with the boundary lines <NUM> (<FIG>) denoting an angular range for light guided by the pupil replication waveguide. Thus, the apodization of the z-profile of the refractive index contrast Δn of the diffraction grating <NUM> of <FIG> lessens the portion of the display light out-coupled into the non-blazed diffraction order <NUM> (<FIG>), to a higher degree tan the refractive index contrast of the blazed portion <NUM>. The behavior of the non-blazed diffraction efficiency <NUM> of the Bragg grating <NUM> is similar to the non-blazed diffraction efficiency <NUM> of the Bragg grating <NUM> of <FIG>.

Referring now to <FIG>, a method <NUM> of manufacturing a pupil replication waveguide includes forming (<NUM>) a plurality of slanted fringes, e.g. the slanted fringes <NUM> of <FIG>, on a slab of transparent material, e.g. the slab <NUM> of <FIG>. The slanted fringes may be configured for out-coupling display light from the slab by diffraction into a blazed diffraction order. For example, the slanted fringes may have a tilt angle selected to increase the amount of light diffracted into the blazed diffraction order, e.g. the tilt angle corresponding to a specular reflection in the direction of the blazed diffraction order. A first substrate layer may then be formed (<FIG>; <NUM>), e.g. coated, on the slab between the slanted fringes to a portion of the fringes height, thereby forming the first grating layer <NUM> (<FIG>). A second substrate layer may then be formed e.g. by coating (<FIG>; <NUM>) on the first substrate layer between the slanted fringes to a portion of the fringes height, thereby forming the second grating layer <NUM> (<FIG>). A third substrate layer may then be formed, e.g. coated (<FIG>; <NUM>) on the second substrate layer between the slanted fringes to at least the height of the fringes, thereby forming the third grating layer <NUM> (<FIG>). The first, second, and third substrate layers together form the substrate <NUM>. A refractive index contrast of the second grating layer <NUM>, i.e. the layer formed by the fringes <NUM> and the second substrate layer, is higher than a refractive index contrast of the first grating layer <NUM>, i.e. the layer formed by the fringes <NUM> and the first substrate layer. The refractive index contrast of the second grating layer is also higher than a refractive index contrast of the third grating layer, i.e. the layer formed by the slanted fringes and the third substrate layer.

The plurality of slanted fringes may be formed by a suitable deposition method, for example standard and /or selective atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and or physical vapor deposition (PVD) in conjunction with plasma etch or vapor etch or wet etch or atomic layer etch (ALE). The deposition may be followed by masked directional etching, for example. In some embodiments, the first, second, and third substrate layers are formed by at spin-on process where polymer materials with suitable refractive indices are spin-coated onto one another, to form a stack of varying refractive index. An intermediate etch or lithographic exposure-and-develop step might be included to control the relative thickness in z-direction as well as in X and Y directions. An inkjet or a flowable deposition process may also be used for this purpose instead of spin-coating.

Referring to <FIG>, a method <NUM> of manufacturing a pupil replication waveguide includes forming (<NUM>) on a slab of transparent material, e.g. the slab <NUM> of <FIG>, a plurality of slanted fringes, e.g. the slanted fringes 708B of <FIG>. The slanted fringes may be configured for out-coupling display light from the slab by diffraction into a blazed diffraction order. For example, the slanted fringes may have a tilt angle selected to increase the amount of light diffracted into the blazed diffraction order, e.g. the tilt angle corresponding to a specular reflection in the direction of the blazed diffraction order. A substrate layer, e.g. the substrate layer 710B of <FIG>, may then be formed (<FIG>; <NUM>) on the slab between the fringes 708B to at least the full height of the fringes 708B. The substrate layer 710B may then be baked (<NUM>) to provide a spatial refractive index variation of the substrate layer 710B in the direction <NUM> of a thickness of the substrate layer, such that the refractive index contrast profile of the diffraction grating 700B formed by the fringes 708B and the substrate layer 710B along the thickness direction <NUM> of the diffraction grating 700B is symmetrical, and the refractive index contrast is larger at the middle <NUM> than at both sides of the refractive index contrast profile.

The plurality of slanted fringes may be formed by a suitable deposition method, for example atomic layer deposition (ALD), chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and or physical vapor deposition (PVD). The deposition may be followed by masked directional etching, for example. In some embodiments, the first, second, and third substrate layers are formed by at spin-on process where polymer materials with suitable refractive indices are spin-coated onto one another. An inkjet or a flowable deposition process may also be used for this purpose.

Turning now to <FIG>, a pupil replication waveguide <NUM> includes a plurality of slanted fringes <NUM> supported by a slab <NUM> of transparent material configured for guiding display light in the slab <NUM> by TIR. Similarly to pupil replication waveguide examples considered above, the slanted fringes <NUM> of the pupil replication waveguide <NUM> are configured for out-coupling display light from the slab <NUM> by diffraction into a blazed diffraction order. The slanted fringes <NUM> have a first refractive index n<NUM>.

A conforming layer <NUM> covers the slanted fringes <NUM> to a uniform thickness. In other words, the conforming layer <NUM> repeats the shape of the slanted fringes <NUM>, encapsulating individual slanted fringes <NUM>, while leaving gaps <NUM> between the individual slanted fringes <NUM>, as shown. The conforming layer has a second refractive index n<NUM>.

An overcoat layer <NUM>, e.g. a polymer layer, fills the gals <NUM> between the slanted fringes <NUM> covered with the conforming layer <NUM>. The top surface of the overcoat layer <NUM> may be flat. The overcoat layer <NUM> has a third refractive index n<NUM>. In some embodiments, the first n<NUM>, second n<NUM>, and third n<NUM> refractive indices fulfill the condition n<NUM><n<NUM><n<NUM>. In the example shown in <FIG>, n<NUM> =<NUM>, n<NUM> =<NUM>, and n<NUM> =<NUM>.

Effectively, the slanted fringes <NUM>, the conforming layer <NUM>, and the overcoat layer <NUM> form three grating layers in the pupil replication waveguide <NUM>: a first grating layer <NUM>, a second grating layer <NUM>, and a third grating layer <NUM> (dashed horizontal lines in <FIG>). The first grating layer <NUM> has the refractive index varying from n<NUM> to n<NUM>, that is, from <NUM> to <NUM> in this example. Thus, the effective refractive index contrast Δn of the first grating layer <NUM> is equal to <NUM>. The second grating layer <NUM> has the refractive index varying from n<NUM> to n<NUM> to n<NUM>, that is, from <NUM> to <NUM> to <NUM> in this example. Thus, the effective refractive index contrast Δn of the second grating layer <NUM> is equal to <NUM>. Finally, the third grating layer <NUM> has the refractive index varying from n<NUM> to n<NUM>, that is, from <NUM> to <NUM> in this example. Thus, the effective refractive index contrast Δn of the third grating layer <NUM> is equal to <NUM>. Therefore, such a configuration also provides an apodized refractive index contrast of the diffraction grating similar to ones considered above, i.e. <NUM> - <NUM> - <NUM>.

Turning to <FIG> with further reference to <FIG>, a method <NUM> of manufacturing a pupil replication waveguide, such as the pupil replication waveguide <NUM> of <FIG> for example, includes forming (<NUM>) the plurality of slanted fringes <NUM> on the slab <NUM> for out-coupling display light from the slab <NUM> by diffraction into a blazed diffraction order, the slanted fringes having the first refractive index n<NUM>. The conforming layer <NUM> having the refractive index n<NUM> is then formed (<NUM>) on the plurality of slanted fringes <NUM>, such that the gaps <NUM> are left between the individual slanted fringes <NUM>. The overcoat layer <NUM> having the refractive index n<NUM> may then be formed (<NUM>) on the conforming layer <NUM>. The overcoat layer <NUM> fills the gaps <NUM> between the slanted fringes <NUM> covered with the conforming layer <NUM>, as shown in <FIG>. The indices of refraction of the slanted fringes <NUM>, the conforming layer <NUM>, and the overcoat layer <NUM> may fulfill the condition n<NUM>>n<NUM>>n<NUM> or, alternatively, n<NUM><n<NUM><n<NUM>.

A variety of manufacturing methods may be employed to fabricate the slanted fringes <NUM>, the conforming layer <NUM>, and the overcoat layer <NUM>. In some embodiments, the plurality of slanted fringes <NUM> are formed by imprinting using a mold and a suitable resin, or anisotropic etching through a photolithographically defined mask. The conforming layer <NUM> may be formed by atomic layer deposition, which enables deposition of conforming films of well-defined uniform thickness. The overcoat layer <NUM> may be formed e.g. by spin-coating, which fills the gaps <NUM> and results in a good uniformity of the upper surface of the spin-coated overcoat layer.

Referring to <FIG>, a pupil replication waveguide <NUM> includes a slab <NUM> of a transparent material for propagating display light in the slab <NUM> by total internal reflection (TIR) from top and bottom surfaces of the slab <NUM>. A diffraction grating <NUM> is supported by the slab <NUM>. The diffraction grating <NUM> includes a plurality of fringes <NUM> suspended in a substrate material <NUM>, e.g. a polymer substrate. The fringes <NUM> are formed by a twisted nematic (TN) liquid crystal (LC) material. In some embodiments, LC molecules <NUM> are stabilized by the polymer substrate material. The fringes <NUM> are slanted for out-coupling display light <NUM> from the slab <NUM> by diffraction into a blazed diffraction order <NUM>. Due to the slant of the fringes <NUM>, a greater portion <NUM> of display light <NUM> is out-coupled into the blazed diffraction order <NUM>, and a smaller portion <NUM> of the display light <NUM> is out-coupled into a non-blazed diffraction order <NUM>.

The TN LC material has an ordinary refractive index nO for light polarized perpendicular to the elongated LC molecules <NUM> of the TN LC material, and an extraordinary refractive index nE for light polarized parallel to the molecules <NUM> of the TN LC material. In some embodiments, a refractive index material of the polymer substrate <NUM> is closer to nO than to nE. For these embodiments, a refractive index contrast for the impinging display light <NUM> polarized in the plane of incidence, i.e. in the plane of <FIG>, has a varying refractive index contrast profile along a thickness direction <NUM> of the diffraction grating <NUM>. This happens because in the TN configuration of the LC material shown in <FIG>, top and bottom LC molecules 1418A are disposed perpendicular to a polarization direction <NUM> of the impinging display light <NUM> and therefore have the ordinary refractive index nO for the impinging display light <NUM>, while middle-thickness LC molecules 1418B are at an acute angle w. the polarization direction <NUM>, and therefore have a refractive index between nO and nE for the impinging display light <NUM>, which is typically higher than the ordinary refractive index nO. Consequently, a refractive index contrast is larger at a middle than at both sides of the refractive index contrast profile, which lessens the portion of the polarized display light out-coupled into the non-blazed diffraction order <NUM>. Due to the smoothly varying twist angle of the TN LC molecules <NUM>, the refractive index contrast profile is typically a smoothly varying function. By selecting proper LC molecules orientation geometry, the smoothly varying function may be made to approximate a Gaussian function.

Referring to <FIG>, a near-eye display <NUM> includes a frame <NUM> having a form factor of a pair of eyeglasses. The frame <NUM> supports, for each eye: a light source subassembly <NUM>, an electronic driver <NUM> operably coupled to the light source subassembly <NUM> for powering emitters of the light source subassembly <NUM> for providing a plurality of light beams, a collimator <NUM> optically coupled to light source subassembly <NUM> for collimating the plurality of light beams, a scanner <NUM> optically coupled to the collimator <NUM> for scanning the plurality of light beams, and a pupil replicator <NUM> optically coupled to the scanner <NUM>. The light source subassembly <NUM> may include a substrate supporting an array of single-mode or multimode semiconductor light sources, e.g. side-emitting laser diodes, vertical-cavity surface-emitting laser diodes, SLEDs, or light-emitting diodes, for providing a plurality of light beams. The collimators <NUM> may include a concave mirror, a bulk lens, a Fresnel lens, a holographic lens, etc., and may be integrated with the light source subassembly <NUM>. The scanners <NUM> may include a 2D microelectromechanical system (MEMS) scanner, for example.

The function of the pupil replicators <NUM> is to provide multiple laterally offset copies of the light beams scanned by the scanner <NUM>, to cover the entire area of eyeboxes <NUM>. The eyeboxes <NUM> denote geometrical areas for placing the user's eyes when a user wears the near-eye display <NUM>. When the user's eyes are located in the areas outlined by the eyeboxes <NUM>, an image of acceptable quality may be displayed to the user. The multiple laterally offset copies of the light beams are provided by the pupil replicators <NUM> to ensure that the area of the eyeboxes <NUM> is wide enough for convenient observation of the displayed imagery by different users. The pupil replicators <NUM> may include any of the pupil replication waveguides described herein, such as the pupil replication waveguide <NUM> of <FIG> including the diffraction grating <NUM> of <FIG>, the diffraction grating <NUM> of <FIG>, the diffraction grating <NUM> of <FIG>, the diffraction grating 700A of <FIG>, the diffraction grating 700B of <FIG>, the diffraction grating <NUM> of <FIG>, and/or the diffraction grating <NUM> of <FIG>. The pupil replicators <NUM> may also include the pupil replication waveguide <NUM> of <FIG>, the pupil replication waveguide <NUM> of <FIG>, the pupil replication waveguide <NUM> of <FIG>, and the like.

A controller <NUM> (<FIG>) is operably coupled to the scanners <NUM> and the electronic drivers <NUM>. The controller <NUM> may be configured for determining the X- and Y-tilt angles of tiltable MEMS reflectors of the scanners <NUM>. Then, the controller <NUM> determines which pixel or pixels of the image to be displayed correspond to the determined X- and Y-tilt angles. Then, the controller <NUM> determines the brightness and/or color of these pixels, and operates the electronic drivers <NUM> accordingly for providing powering electric pulses to the light source subassemblies <NUM> to produce light pulses at power level(s) corresponding to the determined pixel brightness and color.

Embodiments of the present disclosure may include, or be implemented in conjunction with, an artificial reality system. An artificial reality system adjusts sensory information about outside world obtained through the senses such as visual information, audio, touch (somatosensation) information, acceleration, balance, etc., in some manner before presentation to a user. By way of non-limiting examples, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include entirely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, somatic or haptic feedback, or some combination thereof. Any of this content may be presented in a single channel or in multiple channels, such as in a stereo video that produces a three-dimensional effect to the viewer. Furthermore, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, for example, create content in artificial reality and/or are otherwise used in (e.g., perform activities in) artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a wearable display such as an HMD connected to a host computer system, a standalone HMD, a near-eye display having a form factor of eyeglasses, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

Referring to <FIG>, an HMD <NUM> is an example of an AR/VR wearable display system which encloses the user's face, for a greater degree of immersion into the AR/VR environment. The HMD <NUM> is an embodiment of near-eye display <NUM> of <FIG>, and may include similar elements. The function of the HMD <NUM> is to augment views of a physical, real-world environment with computer-generated imagery, and/or to generate the entirely virtual 3D imagery. The HMD <NUM> may include a front body <NUM> and a band <NUM>. The front body <NUM> is configured for placement in front of eyes of a user in a reliable and comfortable manner, and the band <NUM> may be stretched to secure the front body <NUM> on the user's head. A display system <NUM> may be disposed in the front body <NUM> for presenting AR/VR imagery to the user. The display system <NUM> may include any of the pupil replication waveguides and diffraction gratings disclosed herein. Sides <NUM> of the front body <NUM> may be opaque or transparent.

In some embodiments, the front body <NUM> includes locators <NUM> and an inertial measurement unit (IMU) <NUM> for tracking acceleration of the HMD <NUM>, and position sensors <NUM> for tracking position of the HMD <NUM>. The IMU <NUM> is an electronic device that generates data indicating a position of the HMD <NUM> based on measurement signals received from one or more of position sensors <NUM>, which generate one or more measurement signals in response to motion of the HMD <NUM>. Examples of position sensors <NUM> include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU <NUM>, or some combination thereof. The position sensors <NUM> may be located external to the IMU <NUM>, internal to the IMU <NUM>, or some combination thereof.

The locators <NUM> are traced by an external imaging device of a virtual reality system, such that the virtual reality system can track the location and orientation of the entire HMD <NUM>. Information generated by the IMU <NUM> and the position sensors <NUM> may be compared with the position and orientation obtained by tracking the locators <NUM>, for improved tracking accuracy of position and orientation of the HMD <NUM>. Accurate position and orientation is important for presenting appropriate virtual scenery to the user as the latter moves and turns in 3D space.

The HMD <NUM> may further include a depth camera assembly (DCA) <NUM>, which captures data describing depth information of a local area surrounding some or all of the HMD <NUM>. To that end, the DCA <NUM> may include a laser radar (LIDAR), a phase-sensitive depth camera, or a similar device. The depth information may be compared with the information from the IMU <NUM>, for better accuracy of determination of position and orientation of the HMD <NUM> in 3D space.

The HMD <NUM> may further include an eye tracking system <NUM> for determining orientation and position of user's eyes in real time. The obtained position and orientation of the eyes also allows the HMD <NUM> to determine the gaze direction of the user and to adjust the image generated by the display system <NUM> accordingly. In one embodiment, the vergence, that is, the convergence angle of the user's eyes gaze, is determined. The determined gaze direction and vergence angle may also be used for real-time compensation of visual artifacts dependent on the angle of view and eye position. Furthermore, the determined vergence and gaze angles may be used for interaction with the user, highlighting objects, bringing objects to the foreground, creating additional objects or pointers, etc. An audio system may also be provided including e.g. a set of small speakers built into the front body <NUM>.

Referring to <FIG>, an AR/VR system <NUM> includes the HMD <NUM> of <FIG>, an external console <NUM> storing various AR/VR applications, setup and calibration procedures, 3D videos, etc., and an input/output (I/O) interface <NUM> for operating the console <NUM> and/or interacting with the AR/VR environment. The HMD <NUM> may be "tethered" to the console <NUM> with a physical cable, or connected to the console <NUM> via a wireless communication link such as Bluetooth®, Wi-Fi, etc. There may be multiple HMDs <NUM>, each having an associated I/O interface <NUM>, with each HMD <NUM> and I/O interface(s) <NUM> communicating with the console <NUM>. In alternative configurations, different and/or additional components may be included in the AR/VR system <NUM>. Additionally, functionality described in conjunction with one or more of the components shown in <FIG> and <FIG> may be<IMG>distributed among the components in a different manner than described in conjunction with <FIG> and <FIG> in some embodiments. For example, some or all of the functionality of the console <NUM> may be provided by the HMD <NUM>, and vice versa. The HMD <NUM> may be provided with a processing module capable of achieving such functionality.

As described above with reference to <FIG>, the HMD <NUM> may include the eye tracking system <NUM> (<FIG>) for tracking eye position and orientation, determining gaze angle and convergence angle, etc., the IMU <NUM> for determining position and orientation of the HMD <NUM> in 3D space, the DCA <NUM> for capturing the outside environment, the position sensor <NUM> for independently determining the position of the HMD <NUM>, and the display system <NUM> for displaying AR/VR content to the user. The display system <NUM> includes (<FIG>) an electronic display <NUM>, for example and without limitation, a scanning projector display. The display system <NUM> further includes an optics block <NUM>, whose function is to convey the images generated by the electronic display <NUM> to the user's eye. The optics block <NUM> may include pupil replication waveguides and diffraction gratings disclosed herein. The optics block <NUM> may further include various lenses, e.g. a refractive lens, a Fresnel lens, a diffractive lens, an active or passive Pancharatnam-Berry phase (PBP) lens, a liquid lens, a liquid crystal lens, etc., a pupil-replicating waveguide, grating structures, coatings, etc. The display system <NUM> may further include a varifocal module <NUM>, which may be a part of the optics block <NUM>. The function of the varifocal module <NUM> is to adjust the focus of the optics block <NUM> e.g. to compensate for vergence-accommodation conflict, to correct for vision defects of a particular user, to offset aberrations of the optics block <NUM>, etc..

The I/O interface <NUM> is a device that allows a user to send action requests and receive responses from the console <NUM>. An action request is a request to perform a particular action. For example, an action request may be an instruction to start or end capture of image or video data or an instruction to perform a particular action within an application. The I/O interface <NUM> may include one or more input devices, such as a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the action requests to the console <NUM>. An action request received by the I/O interface <NUM> is communicated to the console <NUM>, which performs an action corresponding to the action request. In some embodiments, the I/O interface <NUM> includes an IMU that captures calibration data indicating an estimated position of the I/O interface <NUM> relative to an initial position of the I/O interface <NUM>. In some embodiments, the I/O interface <NUM> may provide haptic feedback to the user in accordance with instructions received from the console <NUM>. For example, haptic feedback can be provided when an action request is received, or the console <NUM> communicates instructions to the I/O interface <NUM> causing the I/O interface <NUM> to generate haptic feedback when the console <NUM> performs an action.

The console <NUM> may provide content to the HMD <NUM> for processing in accordance with information received from one or more of: the IMU <NUM>, the DCA <NUM>, the eye tracking system <NUM>, and the I/O interface <NUM>. In the example shown in <FIG>, the console <NUM> includes an application store <NUM>, a tracking module <NUM>, and a processing module <NUM>. Some embodiments of the console <NUM> may have different modules or components than those described in conjunction with <FIG>. Similarly, the functions further described below may be distributed among components of the console <NUM> in a different manner than described in conjunction with <FIG> and <FIG>.

The application store <NUM> may store 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. Content generated by an application may be in response to inputs received from the user via movement of the HMD <NUM> or the I/O interface <NUM>. Examples of applications include: gaming applications, presentation and conferencing applications, video playback applications, or other suitable applications.

The tracking module <NUM> may calibrate the AR/VR 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 HMD <NUM> or the I/O interface <NUM>. Calibration performed by the tracking module <NUM> also accounts for information received from the IMU <NUM> in the HMD <NUM> and/or an IMU included in the I/O interface <NUM>, if any. Additionally, if tracking of the HMD <NUM> is lost, the tracking module <NUM> may re-calibrate some or all of the AR/VR system <NUM>.

The tracking module <NUM> may track movements of the HMD <NUM> or of the I/O interface <NUM>, the IMU <NUM>, or some combination thereof. For example, the tracking module <NUM> may determine a position of a reference point of the HMD <NUM> in a mapping of a local area based on information from the HMD <NUM>. The tracking module <NUM> may also determine positions of the reference point of the HMD <NUM> or a reference point of the I/O interface <NUM> using data indicating a position of the HMD <NUM> from the IMU <NUM> or using data indicating a position of the I/O interface <NUM> from an IMU included in the I/O interface <NUM>, respectively. Furthermore, in some embodiments, the tracking module <NUM> may use portions of data indicating a position or the HMD <NUM> from the IMU <NUM> as well as representations of the local area from the DCA <NUM> to predict a future location of the HMD <NUM>. The tracking module <NUM> provides the estimated or predicted future position of the HMD <NUM> or the I/O interface <NUM> to the processing module <NUM>.

The processing module <NUM> may generate a 3D mapping of the area surrounding some or all of the HMD <NUM> ("local area") based on information received from the HMD <NUM>. In some embodiments, the processing module <NUM> determines depth information for the 3D mapping of the local area based on information received from the DCA <NUM> that is relevant for techniques used in computing depth. In various embodiments, the processing module <NUM> may use the depth information to update a model of the local area and generate content based in part on the updated model.

The processing module <NUM> executes applications within the AR/VR system <NUM> and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof, of the HMD <NUM> from the tracking module <NUM>. Based on the received information, the processing module <NUM> determines content to provide to the HMD <NUM> for presentation to the user. For example, if the received information indicates that the user has looked to the left, the processing module <NUM> generates content for the HMD <NUM> that mirrors the user's movement in a virtual environment or in an environment augmenting the local area with additional content. Additionally, the processing module <NUM> performs an action within an application executing on the console <NUM> in response to an action request received from the I/O interface <NUM> and provides feedback to the user that the action was performed. The provided feedback may be visual or audible feedback via the HMD <NUM> or haptic feedback via the I/O interface <NUM>.

In some embodiments, based on the eye tracking information (e.g., orientation of the user's eyes) received from the eye tracking system <NUM>, the processing module <NUM> determines resolution of the content provided to the HMD <NUM> for presentation to the user on the electronic display <NUM>. The processing module <NUM> may provide the content to the HMD <NUM> having a maximum pixel resolution on the electronic display <NUM> in a foveal region of the user's gaze. The processing module <NUM> may provide a lower pixel resolution in other regions of the electronic display <NUM>, thus lessening power consumption of the AR/VR system <NUM> and saving computing resources of the console <NUM> without compromising a visual experience of the user. In some embodiments, the processing module <NUM> can further use the eye tracking information to adjust where objects are displayed on the electronic display <NUM> to prevent vergence-accommodation conflict and/or to offset optical distortions and aberrations.

Claim 1:
A pupil replication waveguide comprising:
a slab of transparent material for propagating display light therein via total internal reflection; and
a diffraction grating supported by the slab and comprising a plurality of fringes in a substrate, the substrate having a different refractive index than a refractive index of the fringes;
wherein the fringes are slanted for out-coupling the display light from the slab by diffraction into a blazed diffraction order for directing the display light toward a user's eyes, wherein a greater portion of the display light is out-coupled into the blazed diffraction order, and wherein a smaller portion of the display light is out-coupled into a non-blazed diffraction order, wherein the non-blazed diffraction order is associated with light leaking outside of a display; and
wherein a refractive index contrast profile of the diffraction grating along a thickness direction of the diffraction grating is symmetrical, and a refractive index contrast is larger at a middle than at both sides of the refractive index contrast profile, whereby the portion of the display light out-coupled into the non-blazed diffraction order is lessened.